The second game I created for Windows Phone 7 is "5 in a row". I took the code from the Chain Reaction game and modified the game-engine to support 5 in a row.

The game only supports multiplayer, you can't play against the computer.

You can play the free Trial version.
Trial version lets you play the normal field.
Full version can also play the large field.

Available in the Zune Store:
http://social.zune.net/redirect?type=phoneApp&id=d9683bd3-7a21-e011-854c-00237de2db9e