There are so many programs out there and you can spend hours searching through the Web for one. I decided to put most, if not all, on one page for you like a database.
It's so important if you can have your adolescent attend one of these programs. It not only prepares them for college but it gives them a better chance to be accepted into a really good college program. Admission counselors make a note of this when reviewing a candidate. If money is a problem, contact the college to see if they have need-based scholarships. Some of them do!

1. LEAD (for business) (http://www.leadprogram.org/registration/?type=student)
2. MITES (for engineering) (http://web.mit.edu/mites/www/about/overview.html)
3. For the culinary inclined (http://www.jwu.edu/content.aspx?id=990&linkidentifier=id&itemid=990)
4. For writers (this is in the Northeast) (http://www.albany.edu/writers-inst/webpages4/programpages/nyssywi.html)
5. One of the prominent international programs (http://www.yfu-usa.org/)
6. Another international one (http://www.experimentinternational.org/)
7. More international (http://www.internationalymca.org/GlobalTeens/Home.shtml)
8. And yet another one (http://usa.afs.org/usa_en/home)
9. For minorities (http://www.blackexcel.org/summer-progs.htm)
10. Academic and artistic (http://www.educationunlimited.com/)
11. Academics (http://www.uoregon.edu/~tag/view_program.php?sess_program_id=3)
    
12. Domestic & International (http://www.summerdiscovery.com/)
13. The Arts, creative writing, and more (http://www.teenink.com/summer/)
14. Here is a listing I found of most of the colleges that offer these programs (http://www.sfhs.com/data/files/news/SummerOpportunitiesNews/Summer_Enrichment_Programs.pdf)

Also, take a look at Alternative Break programs for volunteer work.