MatWeb - Material Property Data includes a database of material property data sheets covering plastics, metals, ceramics and other engineering materials. The web site can be used freely without registration but users are required to register to use the advanced features. There is a charge to use some of the advanced features.
NIST Scientific and Technical Databases The NIST Data Gateway provides access to over 80 NIST scientific and technical databases. These databases cover a broad range of substances and properties.The NIST Gateway provides access to free databases created by NIST and PC based database available for sale. Some of the databases included are the CODATA Fundamental Physical Constants, the NIST Ceramics WebBook, and the NIST Chemistry WebBook. Search options for the Gateway include keyword, property, and substance name.