Microsoft One-ups Google Maps
Ok, this is just cool (and no downloads required): http://preview.local.live.com/
Basically, the bottom-half of the page shows your typical overhead map view with street names and/or aerial photos, but it's got a little blue car image overlayed on the map. The top half of the screen shows what you'd be seeing if you were sitting in that car, with front and side views. You can "drive" the car around the map using the arrow keys or your mouse, and if you hold down an arrow key, it does a pretty good job of staying on the streets.
As usual, in the preview version the images are limited to the Seattle area (and apparently SF, been having too much fun in Seattle to try that one though.)