UrbanRail.Net 
Information on subway systems organized by continent, and news, links, literature, and a gallery of general subway information.
http://www.urbanrail.net/TubeMap.com
Provides direct links to route maps from subways around the world.
http://www.tubemap.com
Chris's Transit Pics Website
Showcases photographs of subways, buses, railroads, and monorails from a variety of locations. Also features transportation information for tourists in New York City.
http://www.transitpics.com
Metro Bits
Exploration of subways around the world, including arts and architecture, logos, unique destinations, FAQs and trivia, and pictures.
http://mic-ro.com/metro/
The Subway Page
Maps for subway transit systems from a number of cities all over the world.
http://people.reed.edu/~reyn/transport.html
