In Need of...Good Neighbors

Where: Kentucky, Arizona, and Washington

What: Global Citizens Network brings volunteers into some of the most beautiful but economically depressed areas of the country: Appalachia, the Navajo Nation reservation, and the Quileute reservation on Washington's Olympic Peninsula. Visitors take on such tasks as building fences, writing grant proposals, and planting gardens.

Duration: Eight days

Volunteers pay: $800, which covers meals and a sleeping area on the floor of a community center (GlobalCitizens.org)

In Need of...Animal Lovers

Where: More than a dozen sites across the country

What: Earthwatch Institute matches would-be research assistants with scientists who are studying animals and their natural habitats. A volunteer might record the behavior of wild horses on the Outer Banks of North Carolina or tag terrapins off the coast of New Jersey.

Duration: Most trips last two to 17 days.

Volunteers pay: $950 to $2,650, including meals and shelter, which varies wildly, from tents to country inns (EarthWatch.org)

In Need of...Outdoorsy Types

Where: National parks and other public lands, from Maui to Martha's Vineyard

What: The Sierra Club runs about 90 service trips each year, with participants building trails, repairing meadows, and helping with archaeological surveys.

Duration: One week

Volunteers pay: $350 to $600, which covers meals and accommodations ranging from campsites to rustic lodges (sierraclub.org/outings/national/service.asp)

In Need of...DIY-ers

Where: New Orleans

What: Habitat for Humanity is still building hundreds of homes to replace those destroyed by Hurricane Katrina. And with on-the-job training, even those who've never handled tools can help.

Duration: From one day to as long as it takes

Volunteers pay: Nothing, but they must cover their own lodging. Habitat's Camp Hope, a school that's been converted into volunteer housing, has a summer camp vibe complete with bunk beds and curfew. ($20 a night, including meals; Habitat-nola.org)

For more opportunities, see Volunteer: A Traveler's Guide to Making a Difference Around the World (Lonely Planet) or Volunteer Vacations: Short-Term Adventures That Will Benefit You and Others (Chicago Review).
From the December 2007 issue of O, The Oprah Magazine