Strobist.com - OMFG this site totally rocks for learning how to use your flash.
DG28.com - another good flash site.
Sportsshooter.com - If you are into action shots.
photojojo.com - lots of cool tips and DIY
We are putting together an area on our site with hints and tips to help people with their photography. We have put together information on the basics but still have some work to do on some of the more spcific areas: