Dan Heller's Photography Business Blog - a wonderful journal to read. Plenty of in depth information and articles.
DPReview - perhaps the best place to learn a lot about photography. Top-notch camera reviews and remarkable forums.
Luminous Landscape - a great resource with many tutorials and reviews.
Photozone - any lens you can think of has been tested here.
AfterCapture - magazine with monthly publications for photographic post-production work.
It also provides online multimedia resources for the photographic professional. In addition to archives of AfterCapture’s print articles, it provides original online content, tutorials, blogs, and audio and video podcasts.

If you know of any other good sites you find useful, please leave a comment.