User Photos on Google Street View
The new Street View feature with visualization of user photos is pretty awesome. You can view a nice example here . It's similar to Microsoft's Photosynth, but the integration with Google Maps is much better (and it doesn't require Silverlight). Also, as I understand, Photosynth only took user submitted pictures, while this is based on automatic extraction from sites such as Panoramio, Flickr and Picasa.