Educational Tours/Travel Groups:

Council on International Educational Exchange--one of the best places for a student to start. Highly recommended.

International Student Travel Confederation--very much like above. Worth your time for sure.

International Study and Travel Center--non-profit org with lots of info...visit if for the searchable database of over 1,500 overseas travel opportunities.

STA Travel--a huge group that specializes in student travel. Helps with Eurail, ID cards, and so forth.

US Dept of State/Bureau of Educational and Cultural Affairs--outlines numerous opportunities for overseas educational and cultural opportunities and exchanges.