This has to be one of the coolest app's for cell phones, This free app allows you to use your phone to view the street your looking at, the phone apprantly looks for a photo of what your looking at and overlays it so you can see what it was like 20, 50 even 100 years ago. More in the link below
http://hudsonvalley.ynn.com/content/.../?r=6635449907
...and here's the link to the app, History pin
http://www.historypin.com/