Airliners.net
Site claims to have the largest aviation photo database on the Internet. Search by aircraft name, category, airline and keyword. The site also has aviation statistics and history.

National Portrait Gallery
London's National Portrait Gallery has 21,000 images online, with information on a total of 45,000. You can conduct keyword, artist, or subject searches and retrieve all the available data on related images.

Symbols.com
A fascinating collection of 2,500 Western symbols, searchable by image or word.

TerraFly
Fly over your neighborhood, if you're in the U.S., viewing aerial maps from the U.S. Geological Survey and other sources.