Start with the Basics here!
ETTL Wireless Flash Tutorials
FAQ - EOS Flash (The Bible)
Evaluative vs. Average flash metering
Using fill flash in Av (and Tv) mode and NEVEC (Negative EValuative Exposure Compasation)
Using Hotshoe Flash Units Off-Camera: Here Are the Basics.
Which flash should I get for my EOS camera?
Canon Flash Work (2/2006)
Is my old flash unit safe for my new camera? Here's how to find out.
Trying to compare flash unit specifications? Try this link.
Off-camera flash need not be difficult, nor expensive
Cheap Hot Shoe Warning - Be careful!
Will Crockett DVD - digital ON CAMERA FLASH
Speedlight's and Softboxes: A Compilation Of Related Threads