The Pelagic Shark Research Foundation http://www.pelagic.org/ This research center maintains one of the best shark resources on the net. Learn about their biology and behavior, take a look at numerous shark images, and learn about the research foundation.
Shark Research Institute http://www.sharks.org/ This institute maintains a web page to discuss their numerous research studies and conservation efforts. Their main efforts focus around studies of the whale shark and much information can be found online.
The Shark Research Program http://www.flmnh.ufl.edu/fish/Sharks/Sharks.htm This site discusses the International Shark Attack File and helps to put the reality of shark attacks into perspective. It also includes a comprehensive and helpful resources page.