Google Earth (iTunes Link) for the iPhone/iPod touch is amazing. You literally have the whole world in your hands!
When you first start up the app, you will see the earth. Tap on it a few times to zoom in. Keep tapping to zoom in even further.
Tilt your phone to adjust your view. This is great if you want to see mountainsides.
You can also search for a location on the top left. Or you can let Google Earth find your exact location by tapping at the icon in the lower left.
There’s just so much more to explore. Have fun playing with it!