Where do bugs go in winter? How do I survive in quicksand? These and many more questions answered at How Come?
How Stuff Works is just what it sounds like--and more. I love this site. From how MP3 music works, to how to pick a lock, to how hand grenades work, I can't think of anything this place doesn't try to explain.
Most lipstick contains fish scales! Or so they say at Strange But True. (This might not really be a science site, but it's close.)
If you have logizomechaniphobia, don't go to The Phobia List!! (Logizomechaniphobia, by the way, is a fear of computers.) A useless, but still sometimes interesting, list.
Quiz yourself on everything from water to gravity at Syvum, where the quizzes are rated by age and grade level.
Any site that has both optical illusions and bugs must be pretty good. And they have them, at Atoms and Ants.
I admit the Bubblesphere is for kids who are younger than you, but any site totally dedicated to making bubbles has to be mentioned. There's even a history of bubbles. Also, check out the site called Bubbles.
Cool Science looks disappointing at first glance, but click around, and there's some good stuff.
If you've got Flash set up on your computer, look no further than the colorful, cool, yet still educational "movies" at the funky site called Brain POP. Even a film called "Adding and Subtracting Fractions" is good.
Women scientists? What women scientists? It's time you took a look at 4,000 Years of Women in Science, listing famous women from math and science through history.
Yowza! Spend about a thousand hours with the Brain Boosters--logic, math, reasoning, word games, and riddles--at DiscoverySchool.com.
Look at all the quizzes, tests, puzzles, and other things at this site with the ugly name of Puzz.com.
This one is NOT games you play on the Internet; it's full of games you play with paper and pencil, coins, or other items. You can learn the games by reading the page, and then play them later (not in class!). Clever Games For Clever People
Choose from brain teasers, games, and optical illusions at Brain Bashers.
The games at Fun Brain are often a bit easy, but sometimes it's nice to get all the answers right.
Haven't found what you're looking for? Try the Open Directory Project: