Subway maps for major cities are a necessity for international travelers. I've always tried to find ways to have a digital version handy on my mobile device. Back in the days when I first moved to NYC, I used to keep a Dell Axim PDA on me. I would download a NYC Bus Map as PDF and check it via mobile acrobat.
The folks at PixelBeatPaper out of the UK is bringing major cities' subway maps to Symbian S60 5th edition handsets (i.e. Nokia 5800, Samsung Omnia HD and upcoming Nokia N97). These .Sis widgets are available for: NYC, Tokyo, London, Paris, Portugal, and Santiago. This is huge considering these are full functional interactive maps for free. Having these available independent of data is a major plus. This means you can take advantage your Symbian handset w/o accruing data charges. I only wish this is available for older Symbian S60 3rd edition handsets (ie. N95, N82, etc...)