BUNAC is a good place to start for students interested in work permits to Britain, Ireland, Canada, Australia, and New Zealand. They also run an international summer camp program, as well as volunteer programs in Peru and South Africa.
Dave's ESL Cafe: For teaching English as a second language opportunities around the world
eLAP - Experiential Learning Abroad Programs through ISA - International Studies Abroad.
Idealist.org has a huge searchable database of international jobs and internships organized by geographic area, type of work, and others.
JET Programme: Teach English in Japan in a local elementary, junior high or high school!
Transitions Abroad is a great source for all things international. Find resources on travel, intern, volunteer and work programs