Someone really needs to create the next Tetris since there are only so many variants I can play. DigiPen has an 8-part webcast series on creating a video game to help aid in just doing that. Their game doesn't use XNA but uses DirectX 9.0. Their series covers sound effects, sprites, sprite behaviors, basic overview, and collision detection.
This is a bit too late to enter Dream, Build, Play, but if you need some inspiration on some indy games, check out what games were submitted.