I have started a discussion forum on Facebook, and have so far received a number of great ideas for improving my existing games, as well as some solid concepts for my upcoming Airport Madness 3. You can visit the forum here, but must be signed in on Facebook in order to post.
I like using the Facebook environment as my forum platform. Since everyone's comments are connected to their true Facebook identity, the discussion should remain polite and orderly, with no anonymous posters.