Doppelganger for the iPhone and iPod Touch Video Review
As a kid, I was a big fan of the Concentration-style board games: flip over a card, then try to find a match by flipping over another card. Make more matches than the other players, and you win! Doppelganger brings the same kind of play to the iPhone. Doppelganger is fast-paced, pairing a certain number of cards with a maximum number of missed matches per round. Do well (especially on the bonus rounds) and you'll have more chances on the higher, more difficult levels.
It's fast-paced, simple, and addictive.
Here's a look: