Have a look at this great page from
Wikipedia, listing a whole bunch of common misconceptions. (Of course, Wikipedia has
never been wrong about anything, so it's great to have them here setting the record straight.)
Like for example:
Alcohol doesn't evaporate quickly when you cook with it.
Napoleon wasn't short.
Humpty Dumpty was not an egg.
You can't see the Great Wall of China from space.
People don't only use 10% of their brain.
Sugar won't make your kids hyperactive.
Bats aren't blind.
The list is long, but not exhaustive. It is, however, a pretty good place to start before you head over to where the real action is: The Straight Dope.