Some useful dictionaries and other reference books
The American Heritage Dictionary of the English Language, Third Edition, Houghton Mifflin, 1992. ***Glossary of Indo-European roots. Usage notes. Pictures. 400 word histories.
The Oxford Companion to the English Language, edited by Tom and Feri MacArthur, Oxford, 1992. Articles on every aspect of language, short biographies of language heroes, punctuation, grammar -- a browser's delight, an insomniac's comfort.
The Oxford Classical Dictionary, Second Edition, edited by N. G. L. Hammond and H. H. Scullard, Oxford, 1970. Articles on people (real and mythical), institutions, realia of classical antiquity and classical scholarship.
The Oxford English Dictionary, Second Edition, The world's best dictionary. Complete life histories of words, with quotations. www.oed.com On-line OED
ORIGINS: A Short Etymological Dictionary of Modern English, Eric Partridge, Macmillan, New York, 1981. Brilliant, imaginative (not always right).
WHAT'S WHAT: A Visual Glossary of Everyday Objects, Reginald Bragonier, Jr. and David Fisher, Ballentine Books, New York, 1981. Pictures & names for whatchamacallits and thingamajigs.
Mrs. Byrne's Dictionary of Unusual, Obscure, and Preposterous Words, Josefa Heifitz, Citadel Press, Secaucus, NJ, 1974. Wierd and wonderful words like clinomania, kakistocracy, agnosy, dacrygelosis, ecdemomania, agrostographer. Very funky.
On-line dictionaries:
http://www.lib.washington.edu/research/dic.html On-line Dictionaries.
A WEB of on-line Specialized Dictionaries -- Etymological Dictionaries:
http://www.facstaff.bucknell.edu/rbeard/diction4.html#etymology