Office of Professional Management
http://www.opm.gov/policy-data-oversight/hiring-information/students-recent-graduates
This Program is designed to provide students enrolled in a wide variety of educational institutions, from high school to graduate level, with opportunities to work in agencies and explore Federal careers while still in school and while getting paid for the work performed. Students who successfully complete the program may be eligible for conversion to a permanent job in the civil service.

Peace Corps
www.peacecorps.gov
Peace Corps Volunteers are serving in more than 70 developing nations around the world working in Agriculture Services. Find out how you can live and work in another culture, and have the adventure of a lifetime.

USA Jobs
http://www.usajobs.gov/Help/working-in-government/unique-hiring-paths/students/
More Student Intern Programs

Library of Congress
Internships and Fellowships, Available Online, Student/Intern | Library of Congress (loc.gov)
Remote and in-person internships

National Park Service
http://www.nps.gov/redw/getinvolved/volunteer.htm
Volunteer in National Parks