Norman Koren has written a few interesting photography tutorials. His totorials differ from introductory articles that you get on most of the sites. They are much bigger, deeper, and are filled with links and pictures. For example, “Understanding image sharpness: Digital cameras vs. film” (part 1, part 2) or “The Canon EOS 10D Digital SLR:
Impressions and techniques” (part 1, part 2, part 3).