Halcyon is a game for the iPad by Zach Gage and Kurt Bieg that's part music game and part puzzler. You've got little triangles coming down either side of the screen on various strings, and your goal as the player is to match those up by drawing lines across the strings in the right places. As you play across the strings, the game creates a sort of arrhythmic, atmospheric music that's pretty fascinating, and the triangles show up faster, making things get pretty complicated.
The game makes excellent use of the iPad's touchscreen, and there's a lot of game to enjoy; there are 36 different levels along with 2 different Endless Modes to play. There's no actual multiplayer, but the game is integrated with both OpenFeint and Game Center for leaderboards. The game was a finalist at the Independent Games Festival this past year, so at just US$1.99 (during the current sale), you know it's a quality experience.