I don't understand why no one talks about XNA overhere. XNA 2 is out and not even one post about. You can get it here:
http://creators.xna.com/Education/GettingStarted.aspxAnd it comes with network feature and a few more nice things!
And there are a few good projects around. For example this one:
QuickStartEngine: A free, open-source, easy to use engine
http://www.codeplex.com/QuickStartEngine I already have a stable engine and now I am making a Level Editor for it. And I can honestly say that I am learning a lot and enjoy it! You can a little video of it here:
http://www.youtube.com/watch?v=vc72eYcQODcCheers.