Some homeschoolers http://www.welltrainedmind.com/forums/showthread.php?t=159540 with "mathy" kids are using the CSMP (Comprehensive School Mathematics Program) curriculum . According to Wikipedia, CSMP project produced both the CSMP curriculum and the "Elements of Mathematics (EM) program, a grades 7-12 mathematics program for gifted students." The EM program is available through IMACS
http://www.imacs.org/ . CSMP materials can be freely downloaded from http://ceure.buffalostate.edu/~csmp/CSMPProgram/index.html .

Has anyone tried CSMP and/or Elements of Mathematics?

"To see what is in front of one's nose needs a constant struggle." - George Orwell