We expect that the list of resources linked to this page will grow steadily. You should expect the structure to change periodically as we update it in an attempt to maintain a friendly and usable collection. Mr. Math explains concepts in a fairly straight forward manner and then offers a few problems that can be submitted to him and he claims he'll respond. The site is hampered by the limitations of the media, especially in presenting exponents, not equal signs, subscripts,etc. MegaMath offers mathematical concepts which would supplementcurriculum documents.
Activities here allow students to explore and understand various math topics.
For example, students can learn all about logic, graphs, infinity, algorithms, and mathematical knots through games, activities, plays and problem solving stories. This site houses the Ask Dr. Math archives which are searchable by topic and grade-level. Other features at the site include a problem of the day and problem of the month, links to related newsgroups and puzzle archives. Swarthmore College's Mathmagic provideslinks to math challenges starting at the K-3 level.