I can't recommend any P2P games, but here are a few simple ones that are free:
Touch4: FS5 (FREE)
Now with peer-to-peer gaming over Bluetooth and Wi-Fi in iPhone OS 3.0!!
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Mancala: FS5 (FREE) - Multi-Player Mancala!
Touch Hockey: FS5 (FREE) - Multi-player Air Hockey!
Tic-Tac-Touch:FS5 (FREE) - Multi-player Tic-Tac-Toe!
It looks look Touch4 has P2P, not sure about the others, but if you just wanted to check out the tech for a cheap price this might be a good starting point.