Google has ported Google Earth to the iPhone or iPod touch, and it's such an impressive app that it deserves an Apple ad of its own.
The interface for Google Earth will be familiar instantly to anyone who has used an iPhone for more than a couple of hours. Upon launching the app, you see a photo of the Earth from space. To zoom in, you can either double-tap or use the "reverse-pinch" gesture on the screen. Swiping a finger left, right, up, or down moves the display in the chosen direction, and a two-finger rotation turns the display clockwise or counter-clockwise. There are icons on the display (see screenshot at right) for search, using your current location, changing settings, and realigning the display to North.
Things get more interesting when you tilt your iPhone; the display goes from a flat, satellite-eye view to a 3D-like image. If you're near mountainous terrain, you get a true sense of the topographical features of the land. On many screens you'll see Wikipedia icons, which link you to related Wikipedia articles. Read the rest of this post for more details and a gallery of screenshots.