Reference (Most of the listings below are or were print resources):
Book Review Digest
Books in Print
CCH Tax Research
Contemporary Authors
CQ Researcher  1991+
DISS (Dissertation Abstracts)
Encyclopedia Britannica
Facts on File Reference Suite
Grove Dictionary of Art Online
Grove Dictionary of Music
and Musicians Online
International Medieval Bibliography (c. 400-1500)
Library Literature & Information Science 1980+
LISTA (Library Science)
Merck Index
Literature Resource Center
Mergent Online
Oxford English Dictionary Online
Oxford Reference Online Premium
PaperFirst  1993+
Proceedings  1993+
Reference Universe
Serials Directory 
Valueline Investment Survey
WorldCat
Xreferplus

Other Popular Article Listings:
ArtBibliographies Modern
ATLA (religion)
ERIC (education - CSA)
ERIC (education - EBSCO)
PAIS (public affairs)
Philosopher's Index      
PsycINFO
Social Science Abstracts
Sociological Abstracts

Alphabetical List of Databases
Subject List of Databases