Already mentioned:
http://www.youtube.com/watch?v=o30HZquEnuw (World of Goo)
http://www.youtube.com/watch?v=HfRK5-h0Mlw (LostWinds: Winter of the Melodias)
http://www.youtube.com/watch?v=Vs2aF-1o5aw (NyxQuest Kindred Spirits)
Future release to keep an eye on:
http://www.youtube.com/watch?v=KvJcnVr-9dg (Art Style light trax)
http://www.youtube.com/watch?v=G7f7OZpuffM (bit.trip runner)
http://www.youtube.com/watch?v=allh40GT8s0 (Cave Story)