Don't forget XBL games :) If you have an internet connection, every xbl game has a demo, my favs are:
Geometry Wars
Braid
Pacman CE
Castlevania SotN
Bionic Commando
Undertow
Small Arms
Some of those are Multi-Plat I believe.
Currently Playing: Saints Row 2 | Battlefield 2 | Company of Heroes
Recently Beaten: Gears of War | Super Mario Galaxy | Darwinia | MGS4 | Sam and Max Ep. 4, Portal | Mirror's Edge | Uncharted | Mass Effect
Looking Forward to: Alan Wake | Splinter Cell : Conviction | The Last Guardian | Batman: Arkham Asylum | SMG2 | Mass Effect 2 |