There are many non-governmental organizations, inter-governmental organizations, and nonprofits that provide unique career opportunities. The key is finding the right organization to match your individual interests.
Here are some helpful links to find the organization that's right for you!
www.idealist.org posts job-openings/internships at nonprofit organizations throughout the country. Registration is free, and they will send you a daily e-mail with new job postings that match your interests. Great site!
http://www.jobhero.com/nonprofit-career-guide/ is another useful resource guide on the topic: "Nonprofit Career Resource Guide".
www.npconnect.org/jobs posts job openings across the country.
www.wango.org, the World Association of Non-Governmental Organizations, includes a world-wide NGO directory. You can find NGOs that are interesting to you and link their websites to search for job-openings.
foundationcenter.org, the Foundation Center, has information about philanthropic foundations.
learnhowtobecome.org offers resources for people interested in volunteer work and careers in nonprofit organizations.
www.fpa.org posts job openings with a wide variety of international relations and foreign policy organizations.
www.univjobs.com search engine for job openings (administrative and research-oriented) at universities throughout the United States.