The US Patent & Trademark Office (USPTO) site covers patent history, filing, and classification, with a complete database of U.S, patents allowing full text searching of patents granted from 1976 to present; patents granted from 1790-1975 are searchable via classification. Patents can be viewed as images (TIF format). The USPTO site also offers links to some international patent databases. For trademarks, the USPTO site lets you search for active and inactive U.S. trademarks, with words or numerical descriptors, providing online images of the trademarks, dating back to the late 19th century.
The US Patent & Trademark Office also partners with Google to allow powerful full text searching of all U.S. patents, with PDF images and is highly recommended for first-time users of the patent database.