San Diego Natural History Museum
San Diego Natural History Museum: Shark School: Shark Parts
A very good external anatomy site for sharks in particular.
University of Florida
University of Florida: Fin Features and Measurements of Sharks
Some very specific information on the measurements and identifying characteristics of sark fins.
University of Florida
University of Florida: Head Features and Measurements of Sharks
Good diagrams of the external features and labels of the head of a shark, the largest member of the chondrichthyes class.
University of California
Ucmp: Chondrichthyes
Site gives a quick but decent description of the anatomy of the skin and fins.
University of Florida
University of Florida: Body Features of Sharks
Somewhat shark specific, but a great look at the external anatomy of these cartilaginous fish.