This may not necessarily be your cup of tea, but LocoRoco is by far the weirdist PSP game I've played. I've only played the demo and my next on the list is Mercury 2 (I'm a bit of a puzzle type guy), but you can even play LocoRoco online at
http://www.locoroco.com
Worth a look
And by the way, if you don't have the gig version, i.e. a 32mb card, don't even bother with the Homebrew scene, it aint worth the trouble in trying to downgrade a PSP to 1.50. I only ended up saying f'it because I still ended up having to upgrade to the 3.02 kernel before any of the new games will run. I'll be honest, Sony are likely to win the Homebrew wars eventually, because all new games will require the 3.02 security fixes. Moral of the story, keep your PSP safe.
[EDIT] Having said that, if you do have the gig version, get the Devhook tool and use that to run the 2.71 or 3.02 version of the kernel, that way, you can still keep the 1.50 version (if you do decide to downgrade, since this violates the warrenty anyway), then you're a cool customer.
Paul.