The most economical way to explore a big city is to use their local transit system. Unfortunately, people may avoid doing this, for fear that they will get lost or confused. Now, HopStop.com provides a thread through the Labyrinth of the subway systems of New York, Boston, Chicago, San Francisco and Washington DC. Long Island, Metro North and New Jersey are still in beta.

The site also includes bus connections. Make sure to check out the cool itinerary feature, which shows you how to get from one destination to another. My favorite feature: The Rate It!

Read my comment about the B Line in Boston!