http://earth.google.com/
You need windows, a 3d card and broadband though. :-\
But it's free

Been playing around with it for a few hours now.....I first typed in my postcode and watched the Earth zoom in from space, right up to the top of my house!
Anyway it looks like it has all the features of MS-Autoroute (layers for street names, railways, public buildings etc). So it's good for planning trips to.