The 2005 book "Kids Who Think Outside the Box" by Stephanie Lerner recommends

http://www.computercamps.com/

and

http://www.giantcampus.com/cybercamps/

(which since the book was published discontinued camps but now offers online courses) , and a College Confidential post
http://talk.collegeconfidential.com/9080562-post3.html had some good resources for high school students.