2 of the best games available on the Vita are free on PSPlus right now.  Uncharted: Golden Abyss and Gravity Rush.  Both phenomenal games and hard to put down - must haves...  Wipeout 2048, Hot Shots Golf: World Invitational, Dragon's Crown, Persona 4 G, and Super Stardust are all excellent too.  Batman Blackgate comes out in like 6 weeks or something and looks  killer.  I pre-ordered that after watching 1 gameplay video from E3.  A lot of people loved Zero Escape: VLR.  I couldn't get into it but I know people that think it is best game on PSV.  Those will keep you busy for a bit.  There are a bunch of other PS1 games and PSP games that are great also.  If you like fighting games Samurai Showdown Anthology is EPIC, one of my favorites and it's like 15-20 bucks and you get 6 full fighting games, 1/2 of which are super well done.

Thousand Arms would be such a dream to play on PSP. Just think, you can kiss the girls back when score on a date. Nelsha!

If you don't own a PS3 or a PSP then there's going to be a lot of new content on the Vita for you. A lot of PS3 multiplats or portable spin-offs of PS3 franchises will be completely fresh to you.

I recommend:

PSV

- Persona 4 Golden (Best game on the system and one of my favourite games of all time. Significantly more charming than the PS2 version.)
- LittleBigPlanet Vita (Similar to PS3 version, but it'll be fresh to you.)
- Gravity Rush
- WipEout 2048 (Best portable racer.)
- Uncharted: Golden Abyss (Best portable TPS.)
- Dragon's Crown (Also on PS3, haven't played it but reviews are good.)
- Rayman Origins (Multiplatform, but I always felt it fits portables better.)
- Mortal Kombat
- Zero Escape: Virtue's Last Reward
- Metal Gear Solid HD Collection
- Ragnarok Odyssey ACE (Upcoming.)
- Rayman Legends (Upcoming.)
- Ys: Memories of Celceta (Upcoming.)
- Killzone: Mercenary (Upcoming. Even if you aren't into FPS, give it a try. It'll be the definitive FPS and multiplayer experience on portables.)

PSN

- Limbo
- Guacamelee!
- Jet Set Radio

PSP

- GTA: Liberty City Stories
- GTA: Vice City Stories
- God of War: Ghost of Sparta
- God of War: Chains of Olympus
- SMT: Persona
- SMT: Persona 2 Innocent Sin
- SMT: Persona 3 Portable
- Metal Gear Solid: Portable Ops +
- Metal Gear Solid: Peace Walker

PSOne Classics

- Crash Bandicoot 1/2/3/Racing
- Resident Evil 1/2/3
- Spyro 1/2/3
- Metal Gear Solid
- Tomb Raider 1/2/3/4/5
- Silent Hill
- Pandemonium
- Dino Crisis 1/2 (Not in EU .)
- Xenogears (Not in EU either.
- Vagrant Story
- Toy Story 2
- Chrono Trigger (Not in EU.)
- The Legend of Dragoon (FUCK YOU SCEE)

Final Fantasy!!!!!

PSV
- Final Fantasy X HD
- Final Fantasy X-2 HD

PSP
- Final Fantasy I
- Final Fantasy II
- Final Fantasy III
- Final Fantasy IV

PSOne Classics
- Final Fantasy V
- Final Fantasy VI
- Final Fantasy VII
- Final Fantasy VIII
- Final Fantasy IX
- Final Fantasy Tactics

Exactly how big are the PS1 PSN games?
Would you recommend I get 16GB or more?

Grandia is 849MB. JRPG's tend to be big

All ps1 FF games are over 1GB

Persona 1-3 (PSP) all currently on sale in the European PS Store
Persona 4
Uncharted golden Abyss
Little big planet Vita
Limbo
Hotline Miami
Retro City Rampage

Tons of PS1 classics like the Final Fantasy games (really just buy anything by Square since you said you like RPGs)

That's a cause for concern.  It makes me feel like I should get 32 GB.  The main problem here is that the memory cards are expensive.  I read in another thread (that said that Target is going to be selling the Vita for $200 soon) that you can transfer the data to your computer's harddrive and keep space free on the Vita memory card, but is it really all that practical?  Especially if I only have 4 GB?  I feel like even with that method, 16 GB is the minimum I would feel safe with.

I have an 8gb and I usually just delete the games I'm not currently playing, and I re-download them whenever I want.

16gb will be more than enough space for a few PS1 / PSP / PSN games, althought you'd want a 32gb card if you want them all on at once.

Remeber though. You can only DL a game a certain amount of times before it must be repurchased. I believe its 5