www.hippocampus.org
Many free high school courses, including biology but they don't have chemistry.

Books from www.artofproblemsolving.com are great but not free. However, if you sign up for the website (free) you can access the Alcumus program which is free. It is great! You have to get through 60 diagnostic problems, but after that it is fun. Nice video explanations and then problems.

google MIT OCW for many free courses, there is a section called highlights for high school that points out courses well suited to gifted high school students.

free chemistry course videos here:
http://webcast.berkeley.edu/course_details_new.php?seriesid=2009-B-11006&semesterid=2009-B