If you are considering taking a year off prior to college, or you are looking for an alternative to college, you may find one or many of these sites interesting. 

Africa & Asia Venture (AV)	Africa & Asia Venture (AV) is a not-for-profit social enterprise based in the UK that manages gap year and short-break volunteering programs in the developing world for those aged 18 to 25.
AFS	American Field Service
Alzar Gap	Alzar Gap offers three gap programs for high school graduates in Patagonia, Chile and the American West that focus on leadership development, outdoor adventure and community building.
AmeriCorps	National service organization.
AU Gap Program	Students in American University’s Gap Program participate in an internship (3 days/week) as an integral part of their Gap experience.
City Year	City Year has programs in Boston, New York City, Chicago, San Jose, Providence, Columbus, and San Antonio.  It is a national service organization.
Dynamy	A year-long program of internships and independent living
School of the New York Times - NYC Summer Academy	This hybrid program allows students to study online and in NYC with New York Times journalists and other industry experts who will deepen your understanding of the world, widen your horizons and help you plan for the future.
Habitat for Humanity	Help needy communities around the country build housing.
The Center for Interim Programs	Structured alternatives to formal education
Oxford Advanced Studies Programme	An opportunity for students to spend time in a different cultural and educational environment while pursuing individual academic courses.
Where There Be Dragons	Where There Be Dragons has offered global citizenship and leadership programs in the developing world since 1993. We run small-group Gap Year programs each fall and spring plus full-year options for the particularly dedicated student. Applications are accepted on a rolling basis, yet most programs fill by May 1st.
World Learning	One of the oldest reach out organization in the world.  The Experiment in International Livings is part of their program.
Worldsmart	The VOICES Program fosters global citizenship, creative confidence, cultural competency, employability, and social action.
WWOOF	Worldwide Opportunities on Organic Farms (WWOOF) is a worldwide movement to link visitors with organic farmers, promote a cultural and educational exchange, and build a global community conscious of ecological farming and sustainability practices.
Seamester	For over 40 years, we've consistently delivered outstanding educational experiences for young adults. By combining hands-on education, formal academics with cooperative living and adventure travel throughout the world, we have successfully ignited the inherent leadership skills within thousands of students.

More Resources:
AMERICAN GAP ASSOCIATION
GAP YEAR ASSOCIATION
HIGH MOUNTAIN INSTITUTE