I know I am biased when I say my Canon Speedlite Crash Course DVD is the fastest, easiest way to learn your Canon Flash (it really is BTW), however, for your continuing flash education, Strobist is a necessity. David Hobby’s site contains a WEALTH of information covering off camera lighting. While he himself uses Nikons, the tips, diagrams, techniques are applicable for all. If you own a flash, this should be a regular visit on your blog list:

Strobist