Download is offering the entire library of textures FREE (CC0) in 512px is now offering all their textures for free at 512px resolution with direct download links!

(For ultra crisp HD versions the price has dropped too)

Edit: Updated wording for 512px - licence from non-commercial to CC0 (as of June 2018) !

Regarding 512px being kinda useless - depends on the nature of the project, and how close the camera will be zooming in. I attached a rendered ball using one of the textures at 512px resolution. | Seamless Textures | PBR Materials