ATN Booklists provides over 1,000 booklists of suggested reading.

http://nancykeane.com/rl/#Genres
 

Fact Monster

http://www.factmonster.com/
 

Guysread

This site provides recommendations for great books for guys.

http://www.guysread.com/
 

National Geographic World Online

http://www.nationalgeographic.com/media/world/index.html
 

Wacky Web Tales

http://www.eduplace.com/tales/