Reference information:

Chemical properties, names and structures
PubChem
NIST WebBook
ChemIDplus
MatWeb
ChemExper
NCI Database
SDBS
Merck ChemDat

Safety and toxicology data
ToxNet
ChemFate
Vermont SIRI
Cornell University
Oxford University

Chemistry dictionary
Acronyms Database

Literature
Wiley InterScience
ScienceDirect
ACS publications
Ingenta
Scirus

Patents
United States Patent and Trademark Office
The European Patent Office
Japan Patent Office