Databases, Data Collections, and Reference Works: Materials Science

Biomaterials Properties Database (University of Michigan School of Dentistry's Biomaterials Research Center)
Engineering material properties (Apache Point Observatory).
FIBERSET Composite Glossary - Large list of terms.
Justin Tanks Fiberglass Glossary - Fairly large list of terms from this manufacturer of industrial tanks. Includes some uncommon terms such as alligatoring and intumescent.
LDEF Material Database - Data from NASA's Long Duration Exposure Facility experiment. Site is huge, with descriptions, pictures, graphs, and raw data.
MatWeb's Engineering Material Database - Searchable, free, online materials database created by Automation Creations Inc.
Temperature Dependant Elastic & Thermal Properties Database (JAHM Software, Inc.)
WKA Composites Glossary - A fairly large list of terms from an architectural composites firm. Surprisingly, no architecture-specific terms.
Worldwide Composites Search Engine (Deltronix Enterprises)