Their excellent site has a variety of listings of volunteer opportunities for Quakers and Non-Quakers. There is even a page on student school break volunteer opportunities. There is much to read through, before the listing of volunteer opportunities. It includes a definition of term's section, which is quite helpful when you are looking for just the right volunteer position for you. This site is sponsored by Youth Service America.
Organizations can list volunteer positions.
Surfers can look for volunteer positions by their zip code. It is also possible on this site to register as a volunteer, list your skills, and then potential recruiters can look for you. The U.S. Park Service site is a no nonsense, easy to use location. It provides information on volunteer positions available at U.S. Parks from Alaska, Florida and even Wyoming. The Park Service site has a page with multiple links to information on managing volunteers.