Well you can download the NYC subway maps from the MTA website:
http://mta.nyc.ny.us/nyct/maps/submap.htm
YOu can also dowload a program called Metro. I've been using that program for about 8 years since my old HP Jornada PDA. You can download the maps to the transit system in basically every city and every country that has one and they are updated frequently, although you have to dowload updates yourself. It also includes common landmarks as search items for directions. Check it out.
http://metro.nanika.net/