Materials Lab is part of the School of Architecture at the University of Texas. The Lab has 27,000+ physical samples which are searchable through an online database. According to their website, "All samples in our collection are searchable online by five categories of criteria: composition, form, process, properties, and application. Each entry includes sample images and dimensions, location and availability in our physical library, manufacturer information, and a list of material attributes."
ARCAT is a free resource featuring building product information. Their philosophy is "To publish quality products for architects, engineers and specifiers to enable them to easily specify ARCAT building product manufacturer clients." The website includes product information, manufacture catalogs, and videos. Also, downloadable CAD drawings and BIM Objects.
Transmaterial is a website that accompanies books by the same name written by Blaine Bronwell. According to the website, this online source "intended to be a clear, concise, accessible, and carefully edited resource that provides information about the latest and most intriguing materials commercially available." From the website, you can read about materials organized by type: biomaterials, ceramics, digital, light, metals, and polymers.
Materia is an organization based in the Netherlands that features a global network of over 2,000 materials. From the website, basic information about the materials, like category, properties, and code, can be viewed. To see more information and images, register for a free account.
The California College of the Arts maintains a physical collection that focuses on sustainable, eco-friendly materials. The collection can be searched for material information through the libraries' catalog.