oh god there are so many.. Personally i would love to see Resistance 1 or infamous 1
and other options are Syphon Filter, Getaway, Jak or warhawk
But safe bets would be ICO or Jak 3 or Medevil which has already been announced
Also Sony should consider remastering or remaking vita games, coz there are some real gems that deserve to be played, in my opinion the best killzone game is on Vita 'Killzone mercenaries".
Uncharted golden abyss which could fill uncharted void to some extent.
Freedom wars.. doubt it will come as its a niche title, but hey so was gravity rush so fingers crossed