AmeriCorps: organization information, plus position openings, including internships.
Care Corps Volunteer Program: Many opportunities to join CARE in the fight against global poverty.
Chronicle of Philanthropy: jobs and volunteer info.
Environmental Organizations On-Line: a comprehensive listing of all environmental organizations on the Internet.
Global Volunteers:  Service projects: Child Care, Tutoring, Teaching English, Environmental Work, Construction, Health Care, and more.
No specialized skills needed.
Human Services Career Network 
IdeaList: a comprehensive directory of nonprofit resources.
Internet Non-Profit Center: a listing of donor and volunteer organizations.
Northwest AmeriCorps: information concerning the Northwest Americorps organization.
Peace Corps: information about the Peace Corps organization.
Nonprofit jobs
Non-Profit Times