I am just getting back into game development and I am really impressed with XNA. My only problem is that I want a community based 2d game engine so that I can harness the power of the community. Does anybody know of a good XNA 2d game engine that is currently being supported or Do I just have to write one myself?
FlatRedBall is a good option and is being actively supported. http://www.flatredball.com/frb/
It looks like the engines posted are pretty much your only options for 2D right now. You can find a list of available game engines for XNA at the XNA forums. Ziggyware also keeps a list of engines for XNA, and there are a few more 2D engines listed there. Most of them were posted years ago, and I doubt they are currently being supported. You could also check out DEngine, but it looks like that is still in an alpha stage.
For certain types of games (e.g. tile-based RPG) there are starter kits, such as the RPG starter kit and spaceship game starter kit. If you happen to be developing a game for one of those genres, you could build on those examples.
The Kitae game engine is currently under heavy development @ NullCity.com
It is currently in beta but you can sign up for testing.
Ice Cream is really freaking sweet but last I check still in beta. So its a little bit buggy but, I'm sure once they get an official release going. Its already pretty awesome and pretty damn usable. And it comes with Milkshake , a level / animation editor (So Sweet!)