I have put a new game "Falling Blocks You Move to make Lines" on my site. The game was originally written with Beta 1, but I have finally converted it to be Beta 2 compatible and made the source code available for all on my site.
"Falling Blocks You Move to make Lines" is a Tetris clone (did the name give it away?). Tetris has always been one of those games that is generally considered to be one of the first "baby steps" every new game developer should take. XNA has made taking that first step extremely pleasant. I have written clones of this game before, but I've never been able to start coding game logic so quickly before.
I do plan on creating a series of Tutorials broken up into small parts that will walk through from start to finish how to build a game like this. Until then, have fun looking at the source. I do try to use OO practices, follow my own coding standards and comment the code well so it should be fairly easy to look through.