Bartlett's Familiar Quotations (10th Edition) - http://www.bartleby.com/quotations/
Search three quotation collections: Bartlett's Familiar Quotations (1919), Columbia World of Quotations (1996), and Simpson's Contemporary Quotations (1988). Contains over 86,000 well known quotes.
Oxford English Dictionary (OED) - http://www.kcls.org/erout/goto.cfm?f=oed&d=60
Definitions, pronunciations, and word histories. Usage of modern and historical words traced through 2.5 million quotations.