Wikipedia, the free encyclopedia

Search the Web Search en.wikipedia.org

A phenomenally successful "open source" encyclopedia. It has a very active community of contributers and editors. There are editions in 255 languages. The English "edition" has over 2 million articles. There isn't a single better source available on popular culture and it offers excellent academic content as well.

I use it in particular for technology, science, and history and I am always left somewhat exhausted after using it.