WorldatWork (www.worldatwork.org) is a nonprofit human resources association for professionals and organizations focused on compensation, benefits, work-life effectiveness and total rewards. TIP: View Jobs to see more (than the most recent) positions.
You can search for internships at this site and/or post your resume. Tip: The Browse U.S. Internships links may work better than using the search feature.
Position openings published in regional business periodicals for many areas of the U.S. Many postings for jobs in accounting, HR, marketing, finance, operations management, sales, etc.
LinkedIn is a networking tool to connect with people you know, and the people they know. Use LinkedIn Jobs to see open positions, that relate to your profile, and see who you know at those companies or institutions.