Chemistry Databases on the Web (Classified List): This site is a portal to an extensive array of chemical databases in all areas of chemistry. The first category - General (All Types of Compounds) - lists several freely available websites that provide property data.  Chemistry Databases on the Web is prduced by ChemBioGrid, the Chemical Informatics and Cyberinfrastructure Collaboratory at Indiana University.

ChemExper Chemical Directory: Searchable by registry number, molecular formula, chemical name or synonyms, and substructure, the ChemExper Chemical Directory displays information about chemicals (physical and chemical characteristics, structure, MSDS and more). The ChemExper Chemical Directory contains for now over 200,000 different chemicals, 10,000 MSDS and over 10,000 IR spectra.

ChemFinder.Com: ChemFinder.Com is a portal of free and subscription scientific databases.

ChemSpider: ChemSpider links together compound information across the web, providing free text and structure search access to information on nearly 25 million chemical compounds. It is provided to the community by the Royal Society of Chemistry. 

IUPAC-NIST Solubility Database

Merck Index Online The Merck Index is a resource containing information on chemicals, drugs and biologicals. It contains 11,500 monographs and is updated regularly with new information.

NIST Chemistry WebBook

Organic Syntheses

Sigma-Aldrich Catalog: Chemical catalog with spectra, physical properties, MSDS, and other information. Sigma-Aldrich is a commercial chemical producers catalog that contains a large amount of freely available information about thousands of common chemicals. Searchable by chemical name, chemical substance entries may include CAS registry numbers, NMR- and IR-spectra, boiling point, vapor pressure, safety information, core literature references and more.Allows search by name, molecular formula, CAS registry number, or keyword.