While there are plenty of opportunities for Christian volunteer work, many non-Christian groups also offer rewarding international placements.
The American Jewish World Service, or AJWS, has programs in Africa, Asia and Latin America with placements ranging from two months to a year. AJWS covers airfare and medical evacuation but volunteers cover their own in-country living costs - although subsidies are available if you can't afford to pay for yourself.
AJWS places Jewish volunteers in partner non-governmental organizations in an effort to build their capacity - volunteers should be prepared to pass on their skills and train people upwards. Volunteer projects require a wide range of skills - from organizational development to computers to health care and social work.
Another Jewish volunteer opportunity is with Project Otzma, which places young people on a kibbutz in Israel. Most of the work involves manual labor and community services, although the cost is relatively high.
Potential Muslim volunteers have literally thousands of Muslim charities to choose from, but most volunteering opportunities are local and few can accommodate international volunteers. Not all, however. For example United Muslim Relief recruits volunteers for international missions. In addition to local Muslim organizations, this directory at al-islami may be a good place to start.
While it doesn't offer international mission opportunities, the US-based group Women for Afghan Women has plenty of local volunteer opportunities if the issue of Afghan women is one of your concerns.
Volunteering for Buddhist groups is equally challenging from overseas, but some opportunities can be found on Dharmanet, the website for engaged Buddhism.
Wherever you go, whatever group you join, you'll be helping others and making a difference. And this, at the heart of it, is what becoming a volunteer is all about.