I was going to say what Jamy did. I was going to join right out of high school but couldn't because of the degree thing.
It is a 2 year commitment and you do have to leave family behind. I think you get a 2 week vacation each year. Most of the jobs entail teaching (English, technology, business) or manual labor - building schools, laying waterlines, farming, etc. They do usually require a college degree.
You can request an assignment, but do not get to pass. You may be placed alone in a community, so there isn't a big group around you. You make the wage of the country where you work. When yo get out you get $5K (maybe more now) to get re-integrated into American life, travel, move, etc.
I'm thinking there is an international habitat for humanity program but you would be responsible for getting to the country. They feed and house you once you are there.
Here are some good sites:
Major FAQ: IFRE
Globe Aware - Adventures in Service
Volunteer Work: Volunteer Abroad Programs - International Volunteering Opportunities at GoAbroad.com
You can also check with the Red Cross and a local church.