Etymology
 World Wide Words Page (history, quirks, curiosities and evolution of the English language)
 History of the English Language (HEL) Home Page (everything you ever wanted to know)
 Take Our Word For It (an online weekly etymology magazine;includes a database of word histories, roots, links)

Quotations
 Internet Public Library Quotations Reference (Many hard-to-find links)
 Yahoo's Quotation Index (a goldmine!)

Thesaurus and Dictionary Sites
 Roget's Thesaurus
 Roget's Thesaurus (another version of this classic resource)
 Wordsmyth English Dictionary-Thesaurus
 Webster's Dictionary
 Internet Public Library Dictionary Reference (multiple links!)
 Martindale's Dictionaries and Encyclopedias (every type imaginable - military, medical, hobby...!)
 Merriam-Webster Online Dictionary (search to obtain etymologies, pronunciations, and links to related words)
 OneLook Dictionaries (Indexes 473 dictionaries)