Google unveils Google Earth, previously known as Keyhole, for free. Of course you can upgrade to get additional features, etc. etc., but the free product itself is fairly impressive. Essentially, Google Earth is a program that combines the standard Google Map functions with satellite view and a couple other goodies (like 3-D rendering of buildings and terrain, view perspective, distance measuring, and more).
Or, if the earth isn’t enough for you, explore space in 3-D with NASA’s Planet Quest. View the solar system and beyond, with all sorts of nifty tricks at your fingertips.