It looks like that there are a lot of interest in math in this forum. I found this document compiled by American Mathematical society (AMS) about the high school summer programs/camps. It gives very detailed descriptions which will be useful for choosing a program.

http://www.ams.org/employment/mcbrochure09.pdf

My younger daughter took part of two of the programs on the list PROMYS at Boston U (two years) and COSMOS at UC Santa Cruz. Both are highly recommended.