A popular resource for learning to use your flash, David Hobby does a great job explaining light through case studies based on his work as a photojournalist.
Strobist.com
Peak inside the camera bag of talented photographers from around the world!
Shotkit.com
A primer focusing on the ever dynamic speedlite. Syl Arena's enthusiasm for photography and light makes this a fun and interesting read.
Speedliter's Handbook
If you're nervous about your upcoming lens purchase, use their camera and lens comparison resources to see exactly how sharp it is or isn't.