Monster Hunter Freedom Series. If you haven't played Monster Hunter Freedom one or two to carry your chasracter(s) file(s) over then just get Monster Hunter Freedom Unite. It's really the only game you'll ever need. I have other solid ones but to be honest MHFU ranks up there with some of the best games ever assembled.
I like rock band unplugged, MotorStorm: Arctic Edge (buy this one before Langdell gets to it lol) and both locorocos and patapons
Well, I guess it's time for me to get Unite. I have the first 2 and enjoy them alot. How many more weapon types are there compared to MHF2?
Oh yeah... I played the demo and my friend let me play it once... Awesome game. It's pretty hard sometimes though. Oh, anyone play the Metal Gear Solid Peace Walker demo yet? I just got it last night, I think it just came out.
God of War, The Warriors, Daxter -- those are the ones that jump to mind first. Killzone is pretty neat, but definitely hard. I'm sure I'm in the minority, but I hated Crisis Core almost as much as I hated Dissidia (my worst game purchase this year). Tried the demo of Little Big Planet and was less impressed than I hoped I'd be; same for Monster Hunter (as with many PSP games, awkward camera movement killed it for me). Tried Super Stardust and ended up preferring Meteor Blitz -- ironically, because of the controls. Frankly, it's getting harder and harder for me to justify spending $30+ on a new game for the PSP. I'd rather buy a PC game for a bit more. My last PSN purchase was FF7 as a PS1 Classic -- for $9.99 it seems just about perfect.
I recommend Resistance Retribution, Motorstorm Arctic Edge, Tekken 6, Little Big Planet, GTA Chinatown Wars, God Of War CoO, Pixeljunk monsters and Crisis Core or perhaps Dissidia, don't forget MGS too. I don't exactly recommend picking up AC Bloodlines because it was a let down, got low ratings too.
God of War. It's short, but it's one of the best games I've played. Ratchet and Clank is another good one.