Patapon
This is a cute little game for the PSP... much recommended, if you like odd/unusual games, that is.
The game is highly rhythm-based. You control a small army of "Patapon" (basically creatures that look like eyes on legs) by drumming certain rhythms. For example, at the beginning of the game, the circle button is associated with the sound "pon", and the square button with "pata" (hence the name of the game). Making your warriors advance is done by drumming the sound "pata-pata-pata-pon", and you can make them attack by using "pon-pon-pata-pon". As the game goes on, you get more rhythms and sounds, and gain special items.
I like this game... it reminds me a bit of Locoroco, even though they're completely different.
[Update: Here's a demo video.]