Directories

Current

BirthDatabase  Free Birthday Search
British Telecom  the Phone Book, search for people and businesses in the UK
Pipl  Comprehensive people search
SuperPages  Telephone directory, reverse phone and reverse address lookups
Switchboard  Telephone directory, reverse phone, unlisted and cell phone lookups, area code and zip code lookups
United States Public Records, 1970-2009  on FamilySearch
Zabasearch  Search for people in the USA
Zoominfo  Detailed profiles on over 65 million business people

Historical

Ancestry’s U.S. City Directories, 1821-1989  $
British Phone Books $  British Telecom’s archives of old phone books
City Directories of the United States of America  Comprehensive list of city directories, printed, microfilmed and online, and their repositories in the US
Digital Book Initiative’s City, Business & Commercial Directories Collection  List of online US directories with links
FamilySearch’s WIKI on City Directories  excellent research guide on how and why to use directories to further your genealogy research
Fold3’s U.S. City Directories $  City directories from 22 states, be sure to check miscellaneous
Historical Directories  historical city directories for England and Wales from 1766 to 1919
Old European Phonebooks  is a great resource for anyone with European ancestors. The Library of Congress maintains an extensive collection with some directories that go back decades.
Online Historical Directories  Collection of links to city directories in Canada, Ireland, the UK and US, most free, some $. Great resource for tracking your ancestors between census records.
R.L. Polk & Co’s Directory of Directories  directory of directories published by R.L. Polk in the U.S. and Canada
Urban Maps and City Directories: Correlating Family History into Space And Time  presentation from Frank Southcutt, on the Historical Society of Pennsylvania site
WorldVitalRecords USA Directories Collections $

See Books Online for other sources for directories.