The Ottawa Animation Festival is great. Here are some of my favorites so far (trailers and youTube can't compare with a proper 35mm screening... but it's kind of amazing that you can find almost everything online):
Chris Lavis & Maciek Szczerbowski - Madame Tutli Putli (Canada, 2007)
Trailer above, more info at the NFB website.

Aaron Augenblick - Golden Age (USA, 2007)
Don Hertzfeldt - Everything Will Be OK (USA, 2006)
Trailer. More info at Bitter Films.
SSSR - Zune 'Endless Cookie' (UK, 2006)
Higher res at No Fat Clips!.

Luis Cook - Pearce Sisters (UK, 2007)

Jacques Drouin - Mindscape/Le paysagiste (France, 1976)
Yuri Norstein - Hedgehog in the Fog (Soviet Union, 1975)
Marie Paccou - Un jour (France, 2001)