General work, study, travel, volunteer abroad sites:

• IIE's searchable Study Abroad database the best source for information about specific opportunities
• GoAbroad 
• Studyabroad.com 

• University of Minnesota's International Center program search 
• USC's great site with world university links and all kinds of other things
• World Teach, Inc.
• Peace Corps. 
• People to People International Internships  
• Council on International Educational Exchange work 
• BUNAC (work programs in Britain)  
• Enlace (Electronic Network for Latin American Careers and Employment) 
• U of Michigan's great site for work and volunteer opportunities abroad 
• USC's excellent site including research materials

• Volunteering abroad 
• Global Volunteer Network

Sites about teaching English:

• The English Job Maze
• Dave's ESL Job Board 
• TEFL's homepage 
• ESL Employment

Major fellowship opportunities abroad:

• Luce 
• Rhodes 
• Marshall 
• Gates
• Rotary 
• Fulbright 
• Mortimer Hays-Brandeis 

Other Resources:

• Mobility International:  resources for students with disabilities
•  Transitions Abroad - a magazine with all kinds of useful listings
• The International Educator 
• Resources for Gay Lesbian and BiSexual Students 

Student magazine on study abroad: "The Glimpse"