CRC Handbook of Chemistry and Physics: provides chemical and physical property data for a large number of chemical substances.
Lange's Handbook of Chemistry: covers the entire field of chemistry with facts, figures, values, tables, and formulas.
The Yaws Handbook of Thermodynamic Properties for Hydrocarbons and Chemicals
Handbook of Physical-chemical Properties and Environmental Fate
International Critical Tables of Numerical Data, Physics, Chemistry and Technology provides data on physical, thermodynamic, and mechanical properties of chemicals.
Polymer Handbook: almost 2000 pages, brings together all the data needed in theoretical and experimental polymer research
Handbook of Lipid Research: v.1. Fatty acids and glycerides - v.2. The fat-soluble vitamins - v.3. Sphingolipid biochemistry - v.5. The Phospholipases - v.6. Glycolipids, phosphoglycolipids, and sulfoglycolipids - v.7. Mass spectrometry of lipids - v.8. Lipid second messengers
Composite Index for CRC Handbooks: provides an index to the various handbooks published by CRC.
Journal of Physical and Chemical Reference Data: Provides critically evaluated physical and chemical property data, fully documented as to the original sources and the criteria used for evaluation, preferably with uncertainty analysis.
Landolt-Bornstein An extensive collection of critically evaluated physical & chemical data published in over 400 volumes.
Thermophysical Properties of Matter: A 14 volume collection of data on: Thermal conductivity, Specific Heat, Thermal Radiative Properties, Thermal Diffusivity, Viscosity, Thermal Expansion, and Master index to materials and properties.
SciFinder: (Individual Account Required): provides experimental and predicted properties for millions of substances indexed in CAPlus. Tip for searching: Use Explore substances to find the CAS substance record and then click on the registry number to display the tables of experimental and predicted properties.
PubChem (National Library of Medicine): NLM database of compounds, substances, and bioassays, focusing on the biological activities of small molecules. PubChem provides substance information, compound structures, and bioactivity data for small molecules in three primary databases, PCsubstance, PCcompound, and PCbioassay.
NIST Data Gateway: Links to selected online NIST databases (both free and those available for purchase). .
NIST Chemistry WebBook: provides access to thermochemical, thermophysical and spectral data for selected chemical substances.
Chemspider: provides data on physical, thermodynamic, and spectra data.
MatWeb: Data sheets of thermoplastic and thermoset polymers such as ABS, nylon, polycarbonate and others; metals such as aluminum, cobalt, copper and others; ceramics; plus semiconductors, fibers, and other engineering materials.
Physical Properties Sources Index (PPSI): A comprehensive index of physico-chemical and other material properties in both web and print resources. Swiss Federal Institute of Technology Zurich.
PolyInfo: Polymer properties, structures, names, processing, and methods. ~100 types of properties including thermal, electrical and mechanical are range searchable.
WolframAlpha: Provides "dynamic computations based on a vast collection of built-in data, algorithms, and methods." Information on solution chemistry.
Thermolit "NIST Literature Report Builder for Thermophysical and Thermochemical Property Measurements". Thermolit gives you the conditions for the measurement and the full literature reference, but NOT the actual property value.
Kaye & Laby Tables of Physical & Chemical Constants: Contents of the 1995 edition, containing tables of data, formulas, graphs and charts. Fundamental constants to fibre optics, superconductivity to Raman spectroscopy, etc. Reviewed and updated at the (UK) National Physical Laboratory.
Data & Property Calculation Websites: Listings of Data Sites, Calculation/Program Download Sites, Organizations, and a brief bibliography.