Carnegie Museum of National History
http://www.clpgh.org/cmnh/index.html
There's always something happening at the Carnegie Museum of Natural
History.  The Carnegie Museum of Natural History's online exhibitions share the wonders of the museum with the world at large. 

Natural History Museum of Los Angeles County
http://www.lam.mus.ca.us/lacmnh/
This museum was constructed for the World’s Fair and houses a huge collection of birds, insects, prehistoric fossils, marine life, and more.  At this site you can find examples of habitats from around the world.

Bishop Museum
http://www.bishop.hawaii.org/
The Bishop Museum provides a gallery of exhibits on the natural sciences, a planetarium, and online conservation services.

American Museum of Natural History
http://www.amnh.org/
This museum will take you from diamonds to dinosaurs to the depths of the sea.  Select one of the many exhibits and create your own tour. 

The Dallas Museum of Natural History
http://www.dallasdino.org/ 
The Dallas Museum of Natural History is the only collections-based, research-driven public natural history museum in the region.  The musuem provides exhibits on paleontology, mammals, birds, fish, rocks & minerals, malacology, entomology, and live animals. 

National Museum of Natural History
http://www.nmnh.si.edu/
This branch of the Smithsonian allows you to browse through online exhibits about current ecological issues, undersea life, gems and minerals and much more.