Here are some great resources on learning the art of photography that I’ve both used and recommend to others consistently.
Beginner: (Great for someone just starting out with no former photography background)
The Digital Photography Book Vol. 1, 2, 3 & 4. – by Scott Kelby
Photo Workshop. – Various Subjects and Various Authors by
Practical Photography Magazine
Intermediate: (Great for the person who knows how use their equipment and wants to improve on subjects.)
Mastering Landscape Photography – By Alain Briot
National Audubon society guide to Landscape Photography 2nd Edition – By Tim Fitzharris
Captured, Lessons from behind the lens of a legendary wildlife photographer – By Moose Peterson
Advanced: (Heavy technical information! based only on film but some of the teachings can be transferred to digital, Great for the photographer who wants to learn from the roots of photography)
The Camera – By Ansel Adams
The Negative – By Ansel Adams
The Print – By Ansel Adams