I've volunteered a few times for DC Habitat. It's a great experience; the staff on-site is professional and helpful, but they also get you right to work. Getting to do real work on houses that local people will live in, and getting to meet the families is a positive and rewarding thing.

Volunteering with Habitat is a great way to bond with family or friends, or build spirit with your co-workers, so volunteer as part of a group.