General Reference Web Sites
About.com - created by a network of expert "Guides"; one of the largest producers of original content on the Web.
Infomine - Scholarly Internet Resource Collections
Internet Public Library - the first public library of and for the Internet community.
Librarians' Internet Index - access reliable, trustworthy, librarian-selected websites.
MIT Libraries - Virtual Reference Collection - organized by subjects, links to many free online resources
Shmoop.com - designed to make learning and writing more fun and relevant for students in the digital age.
Wikipedia - can be a good place for a topic overview; ALWAYS verify information obtained from Wikipedia.
Read why you should NOT use Wikipedia as a source for a research paper:
Cornell University Digital Literacy Resource on Using Wikipedia
Wikipedia Founder Discourages Academic Use of His Creation
Wikipedia: Researching with Wikipedia