National Geographic - Fish
This site offers stunning fish photography and several feature articles.
  
Australian Museum - Fish
Learn about the museum's fish department, search hundreds of species, watch some underwater movies, or try to identify a fish!
 
Bony Fish
Learn about the diet, behavior, habitats, and scientific classification of several fish on this Sea World site. 

Discovery Channel - Sharks
This is a multimedia, interactive guide to a variety of different sharks.