www.wikipedia.org I don't believe this is a good website. The findings/results are sometimes not reliable because anyone can add information.
www.highschoolace.com This site provided educational quiz games, practice tests, and homework help. It was very resourceful, but has been discontinued for some reason.
www.super-kids.com This site has a plethora of links and some of them do not work. It is limited to subject areas. Some of the material does not seem educational.