Robinson Meyer of The Atlantic points out this immersive, 360º panorama of the martian surface as recorded the by the Curiosity rover. It takes advantage of the iPhone's gyroscope and responds to your movements.
Once the page is loaded, hold the iPhone aloft and turn your body left or right. Lift the phone up or down. Walk backwards and forwards for a unique and compelling way to examine a small portion of the red planet.
Note that you've got to view it in Mobile Safari. An app-specific browser, like that in Twitterrific or Sparrow, won't do. If you've been itching for a fun way to show off your iPhone, this should do nicely.