There are an absolute shed load of decent games to get on the Vita, quite a few as well that are PS store only, some have been mentioned above but be sure to check these out:
Hotline Miami
Limbo
Velocity Ultra
Spelunky
Guacamelee
Machinarium
Knytt Underground
Sine Mora
Stealth Inc
Oddworld Strangers Wrath
Super Stardust Delta
Lone Survivor
Motorstorm RC
Hustle Kings
Dokuro
All of the above are PS store only and you wont go wrong with any of them!
Hotline Miami
Limbo
Velocity Ultra
Spelunky
Guacamelee
Machinarium
Knytt Underground
Sine Mora
Stealth Inc
Oddworld Strangers Wrath
Super Stardust Delta
Lone Survivor
Motorstorm RC
Hustle Kings
Dokuro
All of the above are PS store only and you wont go wrong with any of them!