A simple XNA based puzzle game for Windows Phone 7
Check out a detailed walk through of the source code: http://christian-helle.blogspot.com/2010/09/writing-puzzle-game-for-windows-phone-7.html
Note: The source code discussed in the walk through article is the very first version of the game and contained a few bugs which later got resolved before I published to the Marketplace and later uploaded to CodePlex