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.

Catalog of industrial supplies from raw materials to motors.

Directory and links to industrial manufacturers, suppliers and distributors by industry.

Catalog for industrial and manufacturing products.

Catalog of supplies covering products from adhesives to welding.

Catalog of products from automotive to electrical.

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