The Nrich Maths Project Cambridge,England. Mathematics resources for children,parents and teachers to enrich learning. Problems,children's solutions,interactivities,games,articles,news.
Purplemath contains practical algebra lessons demonstrating useful techniques and pointing out common errors. Lessons are written with the struggling student in mind, and stress the practicalites over the technicalities. Links and other resources also available.
History of mathematics presented through famous problems, with some exercises and their solutions. Done in conjunction with the Math Forum, the home of Ask Dr. Math.