Learn howCloudy Nights - Great review site and discussion forums.
Yahoo SBIG Group - The best in the world post here. Good info as well.
Yahoo Digital_Astro Group - The place to be for the DSLR imager. Friendly people with lots of advice.
Yahoo EQMOD Group - Learn about the EQMOD.
Yahoo Stark Labs Group - Learn about PHD guiding.
Yahoo DeepSkyStacker Group - Learn about DeepSkyStacker.
Catching the Light - Jerry Lodriguss' great how-to site. Buy the book and really be an expert.
Samir Kharusi's Page - Very Educational.
Starry Wonders Astrophotography - Steve Cannistra's site all about CCD imaging and the techniques involved.
Image Acquisition Lecture - Ewell observatory powerpoint lecture on image acquisition.