I mainly bought my PS Vita because of Ys: Memories of Celceta--a reimagining of Ys IV: Mask of the Sun (big mistake Falcom!). As you can guess I was strongly disappointed in the game and since it was the only one I had my Vita just sat around and started to collect dust. But i did pick it up again one day and started to scroll through the PS network for some other titles I could download onto the system. Now my current library consists of these titles;
Aeternoblade- an interesting game of norse mythology with an anime story/artistic twist.
Ragnarock Odyssey ACE- I've barely played through this game but was still enticed by it.
The Dracula X Chronicles of course

Shock Troopers- to my knowledge this title was an Arcade game, Neo-Geo, or even a Turbo duo title. I can't be sure. But it's a good ol' fashioned top-down shoot 'em up (kinda like Super Contra) with lot's of challenge.
Brandish: The Dark Revenant- Finally! Been out in Japan's PSP market for over four years I believe. Now it's been translated and put on the PS network. I'm still waiting for the other sequels Falcom! Brandish's II and III to be specific.
Muramasa ReBirth- Y'all know this one from the Wii days.
Suikoden- A J-Rpg from the PS1 days. The concept was interesting so I picked it up too. Although I think it's still a bit buggy.
Broken Sword 5 and Broken Sword 5: episode 2.- Loved playing the first game and have been a fan of the series since. Sadly Broken Sword's II, III, and IV are still out of reach and it would be beneficial to the PS Vita to have them on the list as well.
Final Fantasy IV: The Complete Collection.- Got it, worth it.
Final Fantasy V- Just cause.
Final Fantasy VI- Same as above. Just cause.
Final Fantasy IX- It's the only latter half of the series that interests me the most as it's similar to the original games' style.
I have heard that the two PSP Final Fantasy games' I and II: Dawn of Souls is to be ported over to the PS network sometime. Don't know when though. But they'll be added to my Vita library when they are available.