You want to volunteer > International Volunteer Opportunities

Worldwide

Service Civil International - Peace organisation coordinating short and long term voluntary projects worldwide
International Volunteerism Resource Center - It provides useful information about volunteering abroad
eVolunteer.co.uk - Free online resource for recruiting volunteers internationally
I-to-I - Volunteer work abroad, while travelling
ICYE - International Cultural Youth Exchange
JAVVA - Jeunes Actifs dans le Volontariat et les Voyages Alternatifs
MondoChallenge - Sends volunteers to help with development programmes all over the world
Network for Good - Search tool for volunteer placements
NGOabroad
Peace Brigades International - Sends volunteers to areas of conflict, providing protective accompaniment to human rights defenders threatened by political violence
Travel to Teach - Opportunities to volunteer in areas such as English and IT teaching, conservation, eco-tourism and community development
UNVolunteers - Focal point for promoting and harnessing volunteerism for effective development
VSO - International development charity that works through volunteers
Working Abroad - International networking service for volunteers, workers and travellers, which offers the ability to take action for nature and society
World Volunteers - Guide to Humanitarian and Development Volunteering
WWOOF - World Wide Opportunities on Organic Farms
Youth Action for Peace
WorldWide Volunteering 
Médecins du Monde
Médecins sans frontieres
Brot für die Welt - works jointly with local churches and partner organisations in Africa, Asia, Latin America and Eastern Europe
CARE Deutschland-Luxemburg - worldwide emergency and disaster relief work
DED (Deutscher Entwicklungsdienst) - German Development Service
Welt Hunger Life - Sustainable Development
UNICEF
BaseCamp International Centers - Volunteer placements in Africa, Asia and Latin America in the fields of conservation, health, social aid and teaching

Africa

VAD-Togo - Workcamps and volunteer projects in Togo
GEMEINSAM FÜR AFRIKA - United for Africa
Women in Progress - International volunteer programs focus on assisting women in Africa to grow their micro enterprises and become self sufficient through business and IT consulting and training
Volunteer Challenge - Volunteer opportunities in Kenya
Volunteers in Community Development Kenya - volunteering programmes in Kenya
Volunteer Work - Volunteer Abroad - Volunteer International Community Development Africa
Lost Talent Foundation - Volunteer Programme in Ghana
Camara - Volunteering Programmes involving the use of technologies to foster educational development in Africa

Portal do Voluntário - Volunteer opportunities in Brazil
Voluntario Global - Volunteer Placements in Buenos Aires, Argentine
Buenos Aires Volunteer - Placements in social projects, Buenos Aires, Argentine
Inka Magik - Volunteer projects in Peru
FairPlay - Volunteer Opportunities in Peru
ELEP - Experimental Learning Ecuadorian Programme
Volunteer Latin America - Volunteer work opportunities in Central or South America
Un Techo para mi País - Opportunity to work with families who are living in a situation of extreme poverty
VolunteerMatch - Searching machine for volunteer opportunities in USA
GuideStar - Searching machine for volunteer opportunities in USA
Points of Light & Hands on Network - volunteer opportunties in USA
Whatcom Volunteer Center - volunteer opportunities in USA
Jóvenes de Buena Voluntad - International Volunteer Programme in Peru