Bartleby - This site has far more than quotes, you can find full texts here as well - poetry in particular.
Citizendium - This is supposed to be the more “professional” Wikipedia. So far it’s not really taken off, but the information here is often a bit more “elite” but usually not as detailed.
Answers.com - Answers.com is a sort of “commercial” Wikipedia. It makes use of the info on Wikipedia, combined with many other reference sties, to become a one stop shop. It also has a mobile site that I tend to use a great deal.
ePodunk - If you’re looking for information regarding a city or place, it doesn’t get much better than ePodunk.
Encyclopedia Britannica - I know it seems awfully “old school” but this site is an excellent source of information and much more authoritative than Wikipedia.
Scholarpedia - A step up from both Wikipedia and Citizendium in terms of scholarly respectability, it doesn’t have nearly as much information, but the articles have all been written by experts with peer review. An academic paradise!
Okay, two sources that your college probably gives you access to. If you aren’t a student, sorry… but these are too good to ignore. You’ll need to see your local school librarian to see how to access these (or you may have a library website you can access it through.)
JSTOR - You know all those stuffy journals around your professors office? And those articles in your course packets? This is pretty much that. For research it enormously useful.
Oxford English Dictionary - The definitive resource when it comes to the English language. Not just for English majors, the OED (as it’s known) is useful for almost anyone in the social sciences.
Wikiseek - When you absolutely, positively, must have the real thing - WikiSeek is Wikipedia with a better search engine. I would also suggest WikiMindMap for when you’re trying to get a better holistic grasp of a subject.
References for Specific Disciplines
Online Education Database - This is a strange site, and I’m not quite sure what to make of it - but this link lists over 100 specific search and research tools, often relevant to specific subjects.
MathWorld - if you have the great misfortune of having to take math, then this site can be of great help. Everything mathematics from Geometry to Calculus is covered by this site in great detail.
GeoHive and Fedstats - These are both statistics sites, so if you need to know how many people. Fedstats allows public access to public agency statistics. Geohive is a bit cooler, primarily providing global statistics (gender populations, coal reserves, etc). I know, it’s so exciting I can’t stand it.
Glossary of Poetic Forms - This will help you get through that English Literature class. You too can know the difference between a Canto and a Cento.
Now, if you’re in my fields - these next three are excellent resources.
Religion Online - If you are a scholar of religion this is an excellent, excellent resource filled with many primary texts.