Try to save some money while on the road? Use the subway or Tube or S-Bahn instead of a cab or taxi. Granted it doesn't work in many cities and many times the place you stay isn't close to a subway station anyway and you don't like standing in a shaking train after 13 hours of flight. There's plenty of reason why you won't but there's even more reason why you would.
To help those of us who like to use public transport and perhaps also help saving some money for the company if you're a business traveler, Amadeus, "the company behind your travel agency", has put up a list of printable subway maps and more info on subways around the world on http://www.Amadeus.net/home/new/subwaymaps/en/. You can even download maps as PDF or Word document. Thanks Lifehacker for the tip.