Google Earth Flight/Sub/Spacecraft Simulator
Google Earth has had a flight simulator built in for quite a while (hit CTRL-A), but as the Google Earth Blog points out, with the new data available in Google Earth 5, you can also fly under water or on Mars. Just get to wherever you want to fly from, hit CTRL-A and go at it. Top Gun soundtrack not included.
Besides the geek factor, it can be a little easier to navigate over the default interface if you’re using something like a track ball or tablet.