Materials Resource

MatWeb http://www.matweb.com/index.asp?ckck=1 is a site that allows you to look at a number of materials (wood, steel, aluminum...) and search for specific properties or compare types of materials to each other. For instance for wood you can find the density, tensile strength, and other information needed for structural design for a large number of species of wood. While it isn't a source that I refer to often, it has come in handy in specialized applications.