Although not an official source for patents, Google Patents enables you to find some pre-1976 patents by keyword.

Official database of the U.S. Patent and Trademark Office. You can search the entire text of patents from 1976 to the present. Earlier patents (1790-1975) can only be searched by patent number or classification code.

A complete guide to Penn State's resources for patent searching.

A catalog of electronics components and products.

Catalog of suppliers for electrical components.

Sinks to suppliers, products and services in a variety of subject areas including building, electrical, chemicals, and computers.

Catalog of industrial supplies from raw materials to motors.

Catalog of products from automotive to electrical.

Catalog of hobby supplies for robotics, telescopes, magnets, etc.

Directory of commercial and industrial suppliers and product catalogs.

Links to additional resources for engineering suppliers.