I'd recommend what I have installed right now on mine:
- Shin Megami Tensei Persona 3: Its a jrpg favourite, lots of hours to spend on it, the PSP version is not that bad (though more visual novel oriented) and it even has a female main character option. Also, replayability is pretty nice, trying to discover social links and more gameplay-related stuff. English voice acting is not that bad, though I prefer the Japanese one.
- Monster Hunter Freedom Unite: Who doesn't like this one? Massively popular in Japan, and while its not the latest entry on the saga, its pretty cool to play with friends using the Ad-hoc on PSP or Vitas. Also, 500-or-so quests, that take about 1 hour each, that's a freaking lot of time to spend on it.
- Ultimate Marvel vs Capcom 3: Flawless console port with Cross-playing between PS3's and Vita's. Tons of people playing online, fun and easy to play. Also, pretty nice graphics, the MT framework is pretty good when porting it at lower-spec consoles.
- Mortal Kombat: Another port that's better than the console version, ton-shit of content. Graphics are not as bad, and its using the Unreal Engine 3 for rendering stuff. Its pretty impresive when you think about it. Its looks a little worse than the console version in the characters models though. Also, fun as hell to play online.
- Motostorm RC: Free on the US!
Who cares the rest?