Photo credit: Khan Academy
Khan Academy offers great courses in Math, Science, Engineering, Arts, Humanities, Computing, Economics, Finance, and test preparation. This link will take you to the lessons for Pre-algebra, which includes: arithmetic properties, factors and multiples, reading & interpreting data, measurement, fractions, decimals, negative numbers & coordinate plane, ratios, rates, proportions, equations, expressions, inequalities, exponents, radicals, and scientific notation, and more.