Lastly, the game that's been ported to everything under the sun besides dedicated gaming handhelds (it's even available on iPhone and iPad): Resident Evil 4. I'm tempted to suggest bringing Resident Evil 5 over, but some of its set pieces and over-the-top moments might stress out the hardware too much. On the flipside, Resident Evil 4 is perfect for the PS Vita.
It's familiar, but still new to a number of players. It's compact, but has plenty of content. It's incredibly replayable and never leans on excessive grinding or any other cheap tactics used to keeping you from progressing. It looks great, but doesn't demand a lot from hardware.
While it's been re-released so many times that it's starting to get silly, I can't deny that Resident Evil 4 would be a welcome game on PS Vita. Just, maybe add in co-op for Mercenaries mode?