On PC? There... sadly... really aren't all that many.
I would say Don't Starve is probably the most interesting/good, but I would point to console games like Valkyria Chornicles (water-color cel-shading), Okami (Japanese ink-painting style cel-shading), Shadow of the Collosus, Ico, Dark Souls, The Wind Waker, Dragon Quest VIII, or even 3D Dot Game Heroes.
Oh, and come to think of it... on the PC, I'd have to say the best option is probably Dark Souls. It has some truly fantastic art design. --- "...Blame this on the misfortune of your birth." -Char Aznable
Rayman Origins is also a pretty sweet 2D platforming game with some pretty colorful and original artwork. --- "But though you may find this slightly macabre, We prefer your extinction to the loss of our job."
Kentucky Route Zero, you really have to see it in motion as you play through it. The game has this very different art style and an very surreal almost David Lynch like tone. --- http://www.last.fm/user/akuma634
Just read/watched about Betrayer, upcoming game from makers of NOLF and FEAR. Definitely has a different artistic direction...
http://www.pcgamer.com/previews/betrayer-game-announced-hands-on-with-the-new-fps-from-former-creators-of-f-e-a-r-and-no-one-lives-forever/ --- "How do I get rid of a Trojan Horse?" -Sailor_Kakashi "Leave it outside the gates of Troy overnight." -Davel23