The American Museum of Natural History on New York City's Upper West Side has released AMNH Explorer (free) for the iPhone and iPod touch. This app, funded by Bloomberg, is a tour guide and personal navigation system that allows you to easily traverse the museum's huge collection. You can search for an exhibit by popularity, exhibit hall, or an alphabetical listing, and the app will use the museum's free Wi-Fi to give you step-by-step directions to your intended destination (using either the stairs or elevators). You can also get directions to the closest restroom or exit as well as information about restaurants and gift shops.  We had the chance to try out the app while visiting the museum last Thursday and it worked like a charm.