#1 is Killzone Liberation, this game is the best game for the PSP right now. Gamespot doesn't like it as much as I do , so I think there wrong. The 3rd person birds eye view is great because 1st person shooters don't play well on the PSP with some exceptions. This game has alot of stragety and is just the right diffuculty. Its very fun to play and a must have for any PSP owner.
#2 is GTA, this is amazing on the PSP it has everything the other GTAs have on the other systems its a free roam game and its missions aren't to hard but they are hard enough. The grafics are amzing and this game will keep you going for a very long time, so I think its worth every penny [3, 4, 5 are coming tommorrow]