Texas Association Of Museums
http://www.io.com/~tam/

Texas Tech Museum
http://www.depts.ttu.edu/museumttu/

American Museum of Natural History
http://www.amnh.org/

Smithsonian National Museum of Natural History
http://www.mnh.si.edu/

Smithsonian Institution, with 18 separate museums, and some amazing links
http://www.si.edu/

For Teachers
http://www.smithsonianeducation.org/

For Students
http://www.si.edu/resource/faq/
(“for frequently asked questions about the Smithsonian with links to resources from A to Z.”)