One of my favorite DS (and later every other platform) games ever is Puzzle Quest: Challenge of the Warlords. The game ties all the addictiveness of a pure puzzle game like Bejeweled with my incredible need for loot and stats building into a great RPG.
Now, it's on the iPhone.
It'll cost you $9.99 and it's only the first third of the game, but it should be another great game on the go for Apple's platform. All told, however, it looks like this will end up costing $30 and come in three parts. Such is mobile gaming...
I've been noticing a lot more high-profile releases coming to the iPhone recently. It seems like we've passed the first phase of game development, which was mostly comprised of tech demos and gimmick games, and are now entering the first real "generation" of iPhone gaming.
I also recommend checking out the newly released Rolando, as well. What are your favorite iPhone games?