One of the early high quality match/puzzle games for the iPhone has recently dropped in price all the way down to free. Tatomic originally debuted in October of last year at $4.99 and was well received.

The game is a Tetris variant in which your goal is to group atoms into like-colored chains. The game comes with three gameplay modes and is really well put together. Here is a gameplay video from the Lite version, but there's no excuse to not get the full version which is now free.