Since you are in a bit similar situation to me (as a pc gamer i'm not interested in fpses on ps3) I'd suggest:
Valkyria Chronicles - this game is briliant in the way it revolutionizes sRPG/strategy genre. Only warning is if you are anime hater you won't be happy with story and background.
Wipeout HD - this is really awesome twitch racer with great visuals and amazing music and is bacilly full game release with psn game price.
Folklore - this is unique action title with great story and very interesting settings (i suggest you try demo from PSN), also probably game with best ever created sisaxis usage for ps3.
Super Stardust HD - ages old classic but looks awesomely in 1080p glory and greatly captures the arcade feeling of orginal.
Heavenly Sword - slasher with great story and probably most badass crazy villains ever created. Also as a Wii gamer you might find those sisaxis controlled sequences very interesting. A bit short so don't pay more than 20$ for it.
Flower- very interesting "game" great to relax and watch some beatifull visuals.
Also check Deamon's Souls - i can't tell you much since i haven't bought it yet but it has a lot of praise going around.
For shit and gigles if you find one for 5$ or less pick up a copy of Lair - game isn't even average but it's interesting case to watch how developers envisioned usage of sisaxis controlls in early ps3 games.
As for controler - get one Dual Shock 3 so you have at least one controler with playstation button, and get converters for ps2 pads for gaming with friends
I'd also stay away from Infamous - this game has a lot of hype going but in the end is just another boring sandbox - so you better check demo. And ditto for Fat Princess - one of the biggest dissapointments i have had with PSN games.
PROUD MEMBER OF THE PSP RPG FAN CLUB
