Brewology

Depends on your favorite genre. Ps3 has some great exclusives in each category which are all pretty innovative. Here's my suggestions:

Rpg: Demon's souls(hard , but very rewarding)
Shooter: Killzone 2, MAG
Action: God of War 3( a bit gory though action packed and truly epic)
Adventure: Uncharted 2 (won many game of the year honors)
Puzzle : Heavy Rain (actually interactive storytelling but its , a great expierence)
Family: Little Big Planet (obvious choice)

Good suggestions, I haven't played Demon's Souls yet. I hear it is extremely difficult.

Its not always about the exclusives. The PS3 has some other great games as well. Like Assassins Creed 2 and Final Fantasy 13, both amazing games. Especially MGS4.