The other solution and its one that I use for my Game Flow service is a combination of traditional SQL storage and in memory storage on the server. I then use a Web-Service call to make calls against and retrieve the data I need from in-memory storage.
I used PostgreSQL for my standard SQL and HSQLDB for my in-memory storage. I am currently working on getting weapon options using this type of setup that will allow me to tweak weapons and power-ups without the need of having to update clients.
My idea is to have my game server (which is dedicated) connect to the Game Flow web-service and load all the weapon and power-up options in to memory. I don’t have many weapons and power-ups so this is the best solution for me. Because the weapons are spawned on the server … this solution works well. This also allows me to game balance weapons and power-ups remotely via a web-based interface that I wrote.
The in-memory storage is purely used to keep the latest data in place and make it easier to access … I could also look at an object cache solution like Redis instead.