Flow, Everyday Shooter, PJ: Racers, PJ: Monsters, Echochrome, PJ: Eden, The Last Guy,
I put those it the "unique experience" category of PSN.
With more from Pixeljunk and Flower coming.
Other PSN faves:
Blast Factor + Addon, SSHD, Nucleus (underrated, unique twin stick), Pain (with friends) Dark Mist (import), Siren, Elefunk (frustrating though)
Ones to look out for soon:
Wipeout HD, Fat Princess, Red Baron, Savage Moon