Our latest addition to the "why didn't we think of that?" list is this package of subway maps for the iPod. It's a simple and genius concept: upload the maps into the iPod's photo albums for easy access in times of underground uncertainty. The maps work on all color-screen iPods (formerly iPod Photo) and are absolutely free. New York, D.C., Boston and Hong Kong are currently available, with San Francisco, Chicago and London on the way.
iPod Subway Maps