There's never been a more exciting time to apply for careers in the United States government. It's also never been so easy with the creation of the new Pathways Program.
Here are some links to start your job search:
www.usajobs.gov is the official site of the federal government. You can search for openings by agency, salary, etc. You can find jobs at NASA, the Peace Corps, the Department of Justice, Labor, Agriculture, etc.
www.cia.gov is the official site of the Central Intelligence Agency. Political Science students are good candidates for many of the Analytic Positions. There are also scholarships and internships available.
www.gogovernment.org is a website created by the Partnership for Public Service to help people looking for government jobs.
www.policyjobs.net lists research-oriented policy jobs; must register to access some of the postings, but not for most of the entry-level positions. This is not necessarily working directly for the government, but is closely related to government issues.