NYmom,
The EPGY self-paced math courses are excellent.
Your son should take the AMC 10 next year as it is the gateway exam to the AIME and USAMO exams. He would also be interested in the middle school Mathcounts program (
www.mathcounts.org), where many of the future college mathematicians cut their teeth. The USA Math talent search (
www.usamts.org) provides difficult, monthly problem sets to identify top math students.
The
www.artofproblemsolving.com hosts discussions of interest to ambitious math and science students and also has online courses in specialized math topics. You will also find at the site an article entitled, "The calculus trap," which discusses the standard math curriculum and its inadequacies for top math students. (
http://www.artofproblemsolving.com/R...A_Calculus.php)