I've been debating this question myself. Since my GF has abducted my Wii, I'm left to playing the DS and PSP for modern games. Though I've been doing some serious catching up on my PS2 games (Picked up Yakuza cause Dreddz recommends it highly ).

I'm in the middle of deciding myself.

360:
Blue Dragon
Lost Odyssey
Dead Rising
Lost Planet

Playstation 3:
Disgaea 3
Folklore
Demon's Soul
The Last Guardian
LittleBigPlanet
MGS4
Valkyria Chronicles

Just a smidge of the list I've been forming in my head. I'm mostly waiting for the MegaTen team to pick a side which might be a few more years from now...