Canon just launched a new mini-site dedicated to flash photography with the EOS/EOS Digital + Speedlite combo. It also has a Lighting Techniques section with diagrams and example photos that applies to flash in general.
Also, I strongly recommend that anyone using EOS flash—on film or digital bodies—read NK Guy’s excellent article, Flash Photography with Canon EOS Cameras, on photonotes.org, as many times as it takes to truly understand it. It’s long and complicated, but explains exactly how the whole system works, and has definitely helped me make better flash photos with the EOS system.