National Geographic contains all sorts of articles, pictures, videos, etc. on many different topics, mainly things about science, nature, travel, and history. This is a wonderful site; almost anyone can find something interesting here.
National Geographic Kids contains much of the same types of information as does the regular National Geographic site. The main difference is that it has more interactive material and activities that appeal to the younger generation.
This site contains all sorts of interactive, educational games on many different subjects. The games are a bit more difficult, but are enjoyable and teach all kinds of facts. Use your headphones, as this site has sound.