Free games:
Today i die (interactive poetry)
Don't look back (really hard

GROW Series (Not as intellectual, but really artistic funny and innovative)
DOEO Japanese randomness.
Sprout Nice notepad look and surprisingly pleasant
Karoshi suicide salaryman This one is fucking crazy. Your objetive is to get your japanese stressed salarayman killed. And you'll have to figure out how to do it. Damn funny.
Not-free (link to the demo):
Braid (An amazing mind behind a beautiful game, inteligent as hell puzzles!!) Available for mac too

Crayon physics deluxe (crayon graphics and realistic physics, very nice)
Fez Trailer (Still in development)
And if someone here has got a nintendo wii, download Lost Winds!! It's worth every penny!