Originally Posted by
nyctravelguy
www.mta.info give maps (showing the different subway lines and where each of the stops are - whether or not its an express, etc....) and other good info
and if you are arriving via LGA (and probably JFK), there is a transit information desk downstairs by the baggage claim carousels, at least in United/American's terminal, where you can pick up the subway/bus maps for each of the 5 boroughs...and you can buy a refillable Metro card at the candy/newstand nearby as well.