Encyclopedias
General
Juvenile Encyclopedias
Fact Monster Encyclopedia - Part encyclopedia and part homework helper, this site is divided by subject.
Specialty Encyclopedias
CIA World Factbook - Contains cultural, geographical, and political information for over 250 countries
Emily Post's Online Encyclopedia of Etiquette
Encyclopedia Mythica - Encyclopedia of mythology, folklore, and traditions
Internet Encyclopedia of Philosophy - Peer-Reviewed source of philosophy from all over the world.
IMDB - Internet Movie Database - Information on movies and actors
MusicBrainz - Open source of musical metadata
Symbols.com - Information about symbols, signs, flags, and glyphs