One of my buddies just released Switchit for the iPod. Everyone should check it out/buy it since it is a great game and it is only $0.99.
The idea of the game is that you move tiles to match a pattern. It’s a very simple idea, but things get complicated with the introduction of rotation tiles, switch tiles, bomb tiles, locked tiles, etc. It features 75 levels and several unlockable tile sets to keep things interesting.