Before you guys even hired him, Tom Looman was the man, the myth, the location.
His ZEEF guide and his own tutorials?
This isn’t to slight the help me and mine have gotten from everyone else - you all have been amazing as heck as I pop in and ask something I know nothing about - @boredengineer is amazing for physics, f’r example, but Tom deserves his recognition.
Big shoutout to Zak Parrish’s original UE4 blueprint tutorials on the official youtube channel, back in the 4.0 days! Without them, I would probably never have gotten into making UE4 games so quickly or competently. They started me down this path, and I’ll forever be grateful for it 
Also, Peter Newton’s BehaviorTree/AI tutorial taught me everything I needed to know to figure out the rest of it.
Besides programming, art and design I have been mostly focusing in how can I optimized the workflow and pipeline for all our departments by using Unreal Engine and more. So I had to do a lot of pre research before and during using of Unreal Engine 4. With that in mind this helped me a lot during the process and sharing with the rest of my colleagues at work.
I have been helped by various people so far:
Unreal Engine Blueprint Editor Print Cheat Sheet: https://cdn2.unrealengine.com/blog/BlueprintCheatSheet-1989117414.pdf
I’ve printed this out the first weeks when working in Unreal Engine 4 and gave it to our developer(s) and we each day/week we learned a new useful hotkey which sped up our development process.
Unreal Engine 4 For Unity Developers: Unreal Engine 4 For Unity Developers | Unreal Engine Documentation
To learn about the changes when coming from Unity3D.
Directory Structure: Directory Structure | Unreal Engine Documentation
To learn about what each folder does in your engine and/or your project folder.
Engine Features: Unreal Engine 4 Documentation | Unreal Engine Documentation
To learn about each feature and the howto’s when experimenting or using it in your own project(s).
Content Example: Content Examples | Unreal Engine Documentation
So far the best self-experimenting project out there that. Almost all basic features are exaplained in each own level. Think of Level_Blueprints, Level_Advance_Blueprints, Level_Math, Level_Materials etc. In our studio I have been showing and let all our colleague’s work and experiment with Content Example first before working out their own idea’s.
Swarm Agent Troubleshooting: A new, community-hosted Unreal Engine Wiki - Announcements and Releases - Unreal Engine Forums
This helped me, including those on answershub, in order to set up swarm agent to build lighting with different computers at the sametime.
Lighting Troubleshooting: A new, community-hosted Unreal Engine Wiki - Announcements and Releases - Unreal Engine Forums
Same goes for build Light itself and it’s properties. Knowing what does each light, and how to fix common problems explained in text and pictures.
Asset Naming Conventions: A new, community-hosted Unreal Engine Wiki - Announcements and Releases - Unreal Engine Forums
This helped me by setting up a standard asset naming convention for the project which we have been using for 80% for our project(s). It took a while to adjust the different naming convention but now and days we are used to it.
Using SVN as Source Control: Using SVN as Source Control | Unreal Engine Documentation
https://docs.unrealengine.com/latest/images/Engine/Basics/SourceControl/SVN/SC_SVN_Added_Filese.jpg
This image helped me understand which folder I could ignore on SVN and which was required.
Has been sharing a lot of guides and tutorials and I have been using this material for our game designer to block out the levels instead of using the default WorldGridMaterial from Unreal Engine.
Besides him building Solus Project, he also helped a lot with sharing his UDK knowledge and explained them also in UE4. He shared also in depth about his development process during Solus Project, which gave our team an idea in how to tackle the visual asset side of the scope. He also gave us some great feedback during our development process.
Youtube Introduction to Blueprints (pre v4.7): Introduction to Blueprints (pre. v4.7) - YouTube
This helped us while developing our early prototypes while learning blueprints and the use of it, as designers, artists but also programmers.
Unrealslackers: http://unrealslackers.org/
https://pbs.twimg.com/profile_images/773673411310592002/Fimu9HBL.jpg
When this was created during #Slack, I was there almost 5 days a week and tried to help others with their problems and even reached out to some to help me on my problems. Without knowing I met some during GDC 2016 in San Francisco! The community is now using Discord which is also awesome! But I am not using this on a daily during work.
Since we have been switching to Wwise as our audio engine/plugin this is what helped me to get the software/tool integrated in our project(s).
there is probably a lot more I have been missing during writing this post at the time…
And not to forget,
All my colleagues at Turtleneck Studios, where we share our knowledge and experiences with each other when experimenting new stuff during development!
Hmm I got one Particular Training Video with Zak Parrish I really love to share to Beginners since it does such a awesome Job explaining some very basic Fundamentals. Basicly a must Watch Video if you just start out.
Blueprint Communicationshttps://youtube.com/watch?v=EM_HYqQdToE
For me Personaly I would say eXi´s Compedium since I had a general weakness with Networking and its my goto Resource to lookup if I struggle. The Plugin Development Training Video with Michael Noland C++ Extending the Editor | Live Training | Unreal Engine - YouTube and not a Tutorial but a Simple enough to take apart and Study Source for a custom FEdMode GitHub - coderespawn/haste-plugin-ue4
Edit:
Oh yeah how could I forget Slack/Discord, FB Group Facebook Groups People are a great Learning Ressource 
Theres so many great resources for UE4, but I’d probably have to say that my favorite one is Twitch
To be fully honest with you guys, I never really went to a single documentation page, thread on the forums or tutorial without roughly knowing what I wanted to in advance or without having at least a glimpse of an idea of how to do it - I usually only go to the docs to refresh my memory and/or look at a particular parameter description.
My story started out back when Unreal Tournament was announced (before they moved to their own channel on Twitch), which is also the time where I started to watch the regular community and training/support streams - even though I didn’t consider getting one of those too-cheap-to-steal subscriptions back then with my old potato of a PC. Then GDC happened, Tim announced the Engine going free, and I installed it anyways just to confirm: my PC could barely handle it. This didn’t stop me from sticking my nose in, tinkering with knobs and buttons or even taking part in one or the other Game Jam. Now, years later, I’m still doing the same - I happen to find some cool stuff on the stream, try it out the next time I jump into the Engine.
But if I had to pick, it would probably be the FBX Content Pipeline along with the Physically Based Materials page to get my content imported and look as good as possible (with my humble programmer art 
), where I regularly look up various things that I easily tend to forget (such as the measured values for various PBR materials, see also Sébastien Lagardes blog post “Feeding a physically based shading model”; or the various naming conventions to get Collision imported just right).
Otherwise, +20 to that awesome list @Jeisu compiled…and pretty much every other reference posted here - theres a lot to learn with the Engine, and just as many opportunities and resources to do so.
before this thread gets instantly full & all the good stuff has been mentioned would like to add these
well here: https://forums.unrealengine.com/
haha, so well yeah, learn a lot by helping others, seeing other’s mistakes & how they fix them not to mention the multiple ways to fix problems.
would like to say I’ve probably learned the most from: https://forums.unrealengine.com/showthread.php?127685-November-ue4jam-Nov-10-13th-GO-WITH-THE-FLOW
yes it’s the Game Jams
& a big thanks to all the people that just make their knowledge and experience available for others, it’s Google -> https://www.google.com/#q=unreal+engine+4
and a great big thanks to this guy - Mr Allar himself :http://allarsblog.com/
between his twitch streams, blog etc. An inspirations to us all yes it’s the Hero of the Peole !!!
(which is a word now)
A few things I’ve found really useful:
Mathew Wadstein - YouTube - Mathew Wadstein’s ‘WTF Is’ are great bite size explanations of stuff I might not have used before. Also the short length makes them great for reference too!
AI Templates (Blueprint) - Programming & Scripting - Epic Developer Community Forums <- also super useful AI templates
Joe Wintergreen (joewintergreen) is always tweeting useful things, and will show you how he did anything else if you ask nicely!
Finally, from your good selves, this was a great primer for UE4 Behavior trees - https://docs.unrealengine.com/latest/INT/Engine/AI/BehaviorTrees/QuickStart/
“Panda Studio’s Freebies List”
Thread, which contains a lot of project and tutorials, freely available for the community.
There have been loads of content, posts, videos, etc. that have helped me along the way! Here are just a few I have saved that might prove useful to others:
.](https://www.reddit.com/r/unrealengine/)
How to add buttons dynamically on a UMG widget.
How to create a global variable.
A couple other useful starters for me were all of the Zak Parrish videos. I also occasionally view videos from Mathew Wadstein and plenty of other popular tutorial makers.
This video really helped me out with using splines -
Gotta admit, this nothin’ beats this page. What a great initiative, I’ll say
Jokes apart though, Virtus Learning Hub is possibly the best one-stop shop for novice to intermediate users. And then there’s Matt’s Channel that serves as my Wiki now.
Please let me mention a last one, there are actually so many more people I wanna mention in this.
Please find list of sites and videos that helped me to understand UE4 concepts & gameplay framework.
Free sites:
UE4 Wiki and youtube sites:
Blueprints :
Mathew Wadstein - Mathew Wadstein - YouTube
Romero Blueprints - http://romeroblueprints.blogspot.ca/
2D concepts:
WazzaTuts - WazzaTuts - YouTube
UE4 News:
FPS:
Shooter Tutorial - http://shootertutorial.com/
Third Person:
Mindless Pursuits - Quid Infernum - YouTube
IOS Mobile concepts:
Mhousse1247 - Mhousse1247 - YouTube
General Tutorials:
Tesla Dev
Leo Gonzalez
Virtus Learning Hub
VR:
Kodi Mynatt
Level Design:
http://worldofleveldesign.com/categories/cat_ue4.php
Twitch:
C++:
Buckys C++ Programming Tutorials
Commercial sites:
UE4 topics - pluralsight.com
UE4 topics - Udemy.com
Can I just +1 to everything already listed! 
I use the Documentation Search Daily
http://allarsblog.com/ Setting up Perforce!
http://www.tomlooman.com/ Outlines!
Twitch A ton of great streams to watch
https://www.youtube.com/unrealengine A playlist that rivals a Game of Thrones Season!
and yet so many more… Keep up the awesome community
The Twin Stick Shooter project helped me to get started with UE4
PLZlv_N0_O1gb5sdygbSiEU7hb0eomNLdq/
Can’t really list much else as I’m only starting off with UE4 atm, although the resources posted here seem to be worth looking at.
Time Attack Racer with Blueprints (v4.8)
As it still works (most parts) with the present version of UE4 and this one helped me to learn about UE4 and brang my project to where we are now.
Many thanks!
Daerst has a great set of tutorials on his youtube channel, especially for beginners. Daerst - YouTube
Howdy 
This one on blueprint communication stands out for me since it helps me to truly properly understand.
Blueprint Communicationhttps://youtube.com/watch?v=EM_HYqQdToE
Heres all the tutorials I have gone through so far in my homemade schoooling
Profileing and Optomization
Scripting First Person
http://www.digitaltutors.com/tutorial/2074-Scripting-a-First-Person-Shooter-in-Unreal-Engine
Scripting Gameplay
http://www.digitaltutors.com/tutorial/1861-Creating-Gameplay-Systems-using-Blueprint-Features-in-Unreal-Engine
Intro to Blueprints (v4.8)(Series) (Should Have Started Here)
Blueprint Essentials
Blueprint 3rd Person Game Creation
Moar PArticles
http://docs.unrealengine.com/latest/INT/Videos/PLZlv_N0_O1gYDLyB3LVfjYIcbBe8NqR8t/OXK2Xbd7D9w/index.html
Blueprint Networking
3rd PErson Power Up Game
http://docs.unrealengine.com/latest/INT/Videos/PLZlv_N0_O1gYup-gvJtMsgJqnEB_dGiM4/mSRov77hNR4/index.html
Materials
http://www.digitaltutors.com/tutorial/1646-Introduction-to-Materials-in-Unreal-Engine
Stylized Environments
http://www.digitaltutors.com/tutorial/2234-Importing-and-Rendering-a-Stylized-Environment-in-Unreal-Engine
Sculptris - Dynamically sculpt models
http://www.digitaltutors.com/tutorial/182-Using-Sculptris#play-9012
Styleized Axe model and texture
http://www.digitaltutors.com/tutorial/2337-Sculpting-a-Stylized-Axe-in-ZBrush
Styleized Axe Painting In Quixel
http://www.digitaltutors.com/tutorial/2444-Texturing-a-Stylized-Weapon-in-Quixel-Suite-2#play-56048
Styleized Environment Sculpting
http://www.digitaltutors.com/tutorial/2153-Sculpting-a-Stylized-Game-Environment-in-ZBrush-and-3ds-Max#play-50797
Styleized Environment Textureing
http://www.digitaltutors.com/tutorial/2198-Texturing-a-Stylized-Game-Environment-in-Photoshop
Substance Bitmap To Materialhttps://youtube.com/watch?v=UKQTMHVOMKkhttps://www.youtube.com/watch?v=9W5gHlGq6J0
Substance Painter
SubstancePBR Guide
Bridgeing PAinter and Designerhttps://youtube.com/watch?v=zUP9MAi6CVU
Substance Designerhttps://youtube.com/watch?v=NzKtubDsC9o
Sub Painter Dynamic Layeringhttps://youtube.com/watch?v=hVXroe8e88s
Substance PBR Environments
Introduction to Particle Systems in Unreal Engine
http://www.digitaltutors.com/tutorial/1880-Introduction-to-Particle-Systems-in-Unreal-Engine
AI Basics
Crowd AI
Functional AI
http://www.digitaltutors.com/tutorial/2205-Introduction-to-AI-and-Navigation-Systems-in-Unreal-Engine
Creating Morph Targets in Unreal Engine
http://www.digitaltutors.com/tutorial/1906-Creating-Morph-Targets-in-Unreal-Engine
Puzzle Gamehttps://youtube.com/watch?v=d7JKfbk699Q
Ragdollhttps://youtube.com/watch?v=N1tDjbFXeOo
Lighting
http://www.digitaltutors.com/tutorial/1659-Introduction-to-Lighting-in-Unreal-Engine-4
Particles
http://www.digitaltutors.com/tutorial/1880-Introduction-to-Particle-Systems-in-Unreal-Engine
Post Process Visuals
http://www.digitaltutors.com/tutorial/1886-Introduction-to-Post-Processing-Effects-in-Unreal-Engine
Snow
Twin Stick Shooter
Third PErson To First
User Interface
http://www.digitaltutors.com/tutorial/2085-Creating-UI-Elements-in-Unreal-Engine
Mass Enemies
This website helped me understand PBR texturing better for Unreal 4.
Being a Turkish user the information and the users in this forum(unrealengineturkiye.com) helped me a lot when i first started using Unreal.