Oxford English Dictionary - http://dictionary.oed.com/entrance.dtl

Bartlett's Familiar Quotations - http://bartleby.com/100/

Merriam-Webster Dictionary - http://www.m-w.com/netdict.htm

The DICT Development Group - http://www.dict.org/

Biographical Dictionary - http://www.s9.com/biography/

Language Reference Books - http://www.bibliomania.com/2/3/frameset.html