Math for Morons Like Us :
[ Teens/Mature Teens ] - Covers concepts that are used in algebra and geometry, as well as an overview of calculus terms. Includes explanations on how to use the number line, working with formulas, fractions, square roots, graphs, parallel lines, triangles and areas. Also has a message board and short quizzes.
Mathwizz.com :
[ Kids/Teens/Mature Teens ] - Interactive worksheets and quizzes in basic math, pre-algebra, algebra, geometry, and statistics. Find calculators to compute interest and conversion tools for currency, area, temperature, and other units of measurement. Also runs a weekly math contest.