These are some sites I find helpful, inspirational, or both.

Worlds Finest - The Source for all things DCAU
Inanimate Objects - Casimir's Site, the Michael Phelps of customizers
Mike Danza's Customs - Brilliant work all around
Airmax Animated - great stuff
Iron Cow Productions - Love this guys stuff, I was remiss in forgetting his link initially
Custom Justice Forums - A great message board for Customisers