More than just pictures of electric Brill, Flyer and Pullman buses, trolleybuses.net has some great old street-level shots of many cities in North America.
Seattle is only one of five cities in the United States with a trackless electric trolley bus system. King County Metro operates 159 trolley buses on 14 routes that ply over 70 miles of trolley wire, and travel 2,906,297 miles annually. Last year, Metro found that operating new electric trolleys offered a superior financial scenario to new diesel buses. This is even before considering how much better a trolley performs on Seattle's steep hills, or how much less pollution it creates, being supplied by hydroelectric power. If you want to know a little more about how the system works, see some of the photos posted by a King County bus operator known as VeloBusDriver. Some of these photo sets explain the controls of an ETB, the innards of an ETB—so much cleaner than a diesel but so much more dangerous to poke around in—and aspects of how the trolley wire itself works, including the "special work" necessary for tasks such switching routes or traversing a drawbridge.