This is a fun site I used recently in class with my 3rd graders as we were studying fossils - it's called Dinosaurs and it's on the Smithsonian's Museum of Natural History site. This tidy looking little site is actually jam packed with information about dinosaurs that is very accessible to kids from 2nd grade through high school.
On the Dinosaurs site, kids can learn just about anything they ever wanted to know (and never knew they wanted to know) about dinosaurs. There are tons of great pictures from the museum's archives as well as the many digs and expeditions that supplied the information.
There are some slideshows documenting some of the various digs, as well as some of the more prominent dinosaur collections at the Smithsonian NMNH.
What my 3rd graders were enamored with was an interactive "dinosaur dig". After we studied fossils, looked at some real ones, and then did a little play simulation with some clay and toy skeletons, they were ready for the dinosaur dig. The interactive takes kids through the basic procedures of a dig - from the first clearing of the surface to determine how big the site is, to the use of finer and finer tools to carefully get to the skeleton, to the plastering and transportation of the bones to the museum. Once they have successfully cleared, covered, and transported their "specimen", they then clean it and protect it in the museum's lab. After that they are ready to assemble the skeleton - they can use the clues about the various bones to help them find the proper placement. Once their model is finished, they can see different drawings and representations of what that dinosaur (a Stegosaurus) might have looked like.
This is a really engaging site and very easy for kids and their teachers to navigate. What I really liked was that none of the links take you away from the site - they are all built by the Smithsonian NMNH, so all of the information flows and connects really well.
