Web Math: This site offers arithmetic refresher videos. From basic addition and subtraction to ratio algebra and geometry, it teaches you the steps of finding a solution.
Fact Monster: From the folks at Information Please/Pearson Education comes an attractive, easy-to-navigate reference site. Flash cards, multiplication tables, history timelines, biographies of U.S. presidents...they're all here.
Kid Info: This site categorizes links according to the curriculum covered in most U.S. schools, be it ancient Rome or the solar system. You'll discover online dictionaries and encyclopedias.
Math.com: If you've forgotten what an integer is, you'll need this site's arithmetic refresher courses. From basic addition and subtraction to ratio algebra and geometry, it takes you through the steps of finding a solution.