Dictionary: http://www.onelook.com/ 

Thesaurus:

http://www.thesaurus.com

KidsClick!
“Created by a bunch of librarians.” Sites are annotated with reading levels. Selection Policy and search strategy hints are given.        

Awesome Library 
Over 17,000 reviewed resources, selected  for teachers, kids, teens, parents, and librarians

Yahooligans
Browsable, searchable directory of Internet sites for kids, approved by educators

Librarians' Index to the Internet 
Over 8,500 sites selected by librarians, with selection criteria

Internet Public LibraryYouth Division
A directory of sites selected for children 4-11, their parents and teachers (no search capability)

Ask Jeeves for Kids 

Searches database of selected sites

Internet Public Library Teen Division
A directory of sites selected for teens

Berit's Best Sites for Children
Recommended web sites are reviewed and given ratings, now with search capabilities

ProQuest/eLibrary

Evaluated and organized 100,000 links on over 10,000 subjects. Updated daily.

Education World
A search engine for educational Web sites only; now over 500,000 sites

 www.4kids.org
A great starting place for teachers, librarians, and parents

Cybersleuth-Kids
An Internet search guide for the K-12 student

 Genie Find Kids
a "human edited" search engine