Homework Central No, this site won't do your homework for you, but it has some helpful links.
Academic Assistance A free service offering help in a variety of disciplines.
Aufbaul An extensive and somewhat unconventional on-line resource for tutorials and exercises. Although aimed at British middle-school students, this will likely be suitable for high school and college students in North America.
ChemTutor Basic help for high school and college chemistry students.
ChemTeam A solid chemistry course with plenty of links.
Chemistry Coach A collection of great links for high school chemistry.