Science

Science Net
http://sciencenet.tpl.toronto.on.ca
According to project coordinator, Science Net brings together K-12 education resource links and classifies by the Dewey Decimal system, creating virtual library shelves. The site will eventually have eight subject gateways: physics, biology, botany, zoology, geology, paleontology, and astronomy. It is further broken down by target audience: teachers, K-6, and 7-12.
Why Files (Science Behind the News)
http://whyfiles.org
Topics vary greatly, but its stories are timely and authoritative. Sponsored by the University of Wisconsin Graduate School.
How Stuff Works
http://www.howstuffworks.com
Teaches about how things in the world around you work. Examples include cell phones, water towers, suntans, power grids, etc.
 
NMNH Virtual Tour
http://naturalhistory.si.edu/VT3/
Sponsored by the National Museum of Natural History, this site offers insight into the Smithsonian's various collections. The tour is arranged by floor and department, e.g. dinosaurs, fossils, etc. are on the first floor.

Dinosaurs

Dinosaur Exhibits of the National Museum of Natural History
http://paleobiology.si.edu/dinosaurs/
Sponsored by the National Museum of Natural History, this site offers insight into the Smithsonian's large dinosaur collection.
 
 

Endangered Species

Endangered Species Program
http://endangered.fws.gov
Species information from the U. S. Fish and Wildlife Service.  Indexes include: major groups (e.g. flowering plants, vertebrate animals); U.S. regions; and foreign species.  Searches can also be conducted by either scientific or common name.  For each species there is a regulatory profile and in some cases a color photograph and links to other sites.
 
IUCN List of Threatened Species
http://www.redlist.org
Database is maintained by the World Conservation Monitoring Centre.  Information can be searched by entering species or common name. Other searches include: all species within a family, order or class; country; and threat category.
 

Astronomy and Space Sciences

The Galaxy Page
http://www.seds.org/messier/galaxy.html
Site is an excellent starting point to learn about space exploration.  Includes tours of the solar system and high quality links to astronomy and astronautics sites.
Cosmic Origins
http://cor.gsfc.nasa.gov/
NASA's Origins Program seeks to answer two enduring human questions that we once considered around ancient campfires, yet still keep alive in today's classrooms:  Where do we come from?  Are we alone? This site brings together the information gathered through NASA's ground- and space-based observations of the universe.  It includes a library of documents and education resources.
NASA's webpage
http://www.nasa.gov
The official website of NASA this page includes information on current programs, history, and links to NASA's other websites which provide information such as a virtual tour of the International Space Station.
SEDS: Students for the Exploration and Development of Space
http://seds.org
Includes links to SEDS chapters, as well as the Space Images Archive, Space Technology Transfer, Mars Exploration Page, Lunar Resources, Shuttle Schedule, and links to Visions of the Future and other sites on astronomy, rocketry and resource guides.