MatWeb
MatWeb is a database of material properties including data on thermoplastic and thermoset polymers such as ABS, nylon, polycarbonate, polyester, polyethylene and polypropylene; metals such as aluminum, cobalt, copper, lead, magnesium, nickel, steel, superalloys, titanium and zinc alloys; ceramics; semiconductors, fibers, and other engineering materials. It contains information on the properties of more than 76,000 materials