I played the web-based PC version of this puzzler and got pretty addicted - it might look like a match-the-colours game, but it's not. It is however very good, very playable in the easy to play but difficult to master mould of so many classic games. The graphics don't look anything special but the gameplay is immediately accessible and very rewarding when you manage to play it well. At only $0.99 for the iPhone version you're getting terrific value for money.
DropZap web-based version
Buy DropZap on iTunes