Tatomic came to my attention the other day, and I finally gave it a shot this afternoon -- it's terrific. They've done what all game companies should do (and what Apple really needs to support on the actual App Store) and provided a free version [iTunes] to test out, and I can't really recommend it any more highly. It's a falling block game basically, very much like Lumines (which I really enjoy on Xbox Live) -- little spinning atom blocks drop in pairs, and you've got to match them up in certain numbers to clear them off the board. Pretty addictive gameplay, too -- the fact that you've only got two blocks dropping makes it simple, unless things start to pile up, and then you've really got to start thinking what goes where.
Controls are also done pretty well, but take a little getting used to (you basically touch corners of the screen to move, drop or turn the little atoms you're matching), but once you figure them out, you'll start dropping blocks like a maniac. If you finish up the first ten levels and still want more, there's a $4.99 version with three modes and thirty levels total. Excellent puzzler gameplay. I still would like to see a deeper game on the App Store, but for cheap puzzle thrills, Tatomic delivers.