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.