Information Please Almanac http://www.infoplease.com
The Old Farmer's Almanac http://www.almanac.com
Little Exploreres Picture Dictionary http://www.LittleExplorers.com/dictionary.html
Mirriam Webster Dictionary Online http://www.m-w.com
OneLook Dictionary http://www.onelook.com
Online Dictionaries http://www.dictionary.com
The Oxford English Dictionary Online http://www.link.cs.cmu.edu/dougb/rhyme-doc.html