Juniors and Seniors:
Here's a web page I have come upon that has information regarding U.S. Federal Internship programs. One thing that seniors who will soon be in the job hunt for a full-time job might consider is the Federal Career Internship program (FCIP) which from my readings, is a way for the Feds to get grads into jobs that have strong career paths. For example, the FDIC uses FCIP to recruit entry level bank examiners to their Washington office.
http://www.makingthedifference.org/federalinternships/employmentprograms.shtml