If you’re like me, you travel a lot in different cities.  Even though I grew up going to New York City every other weekend, I still don’t know the most efficient way between two points.  A good solution to this issue is the site HopStop: sort of a Mapquest of Google Maps for commuters.  You type in your current location and your destination in New York City (or several other cities) and HopStop provides the most efficient way to take the subway (including walking directions).