Behind the Lens is George Barr’s excellent blog, in which he speaks a lot about composition and the thinking side of photography. George loves industrial photography in a way that I never will, but the difficulty of the subject and his preference for monochrome really refines compositional thought, and he has a lot that is interesting to say.
Mark Graf’s Note’s from the woods showcases his beautiful nature photography (shooting for prints and stock) and has a lot of little insights about doing that kind of photography, in addition to technical and artistic details.