1. Wikipedia
2. howstuffworks.com
3. Yahoo Answers
4. Project Gutenberg
5. Internet Archive
6. Reference
7. Answers
8. eHow
9. Britannica
10. About
    

full list via ebizmba

1. Wikipedia
2. Answers.com
3. HowStuffWorks
4. Encyclopaedia Britannica
5. Infoplease
6. Everything2
7. Columbia Encyclopedia, Sixth Edition

full list via oedb.org

Dictionaries and More

1. OneLook
2. RhymeZone
3. Strange and Unusual References
4. freedict.com
5. The New Dictionary of Cultural Literacy
6. Word Spyphones.
7. Slang Site
8. Behind the Names
9. Directory of Occupational Titles
10. Glossary of Real Estate Abbreviations, Terms and Phrases

full list via teachingtips

#1 The OWL at Purdue

#2 University of Houston, Victoria

#3 Encyclopedia Britannica

#4 Internet Public Library (IPL)

#5 Internet Archive

#6 The Ref Desk

#7 Westfield State College Ely Library

#8 Bartleby

#9 U.S. Census Bureau

#10 Modern Language Association

via degreedirectory.org