Google Earth

Okay, this is the coolest thing I have seen on my computer in a very long time.

http://earth.google.com

Go there, download it, run it. You'll be glad you did. Fast internet connection recommended; decent 3D capabilities on your computer required.

Once you've figured out how it works, here are some other cool things you can do with Google Earth:

1. Turn on the "Borders" checkbox to see state lines when you look at the image map. Also turn on "Roads".
   
2. In the "Layers" panel (lower left part of the interface), check the box that says "3D buildings" and then zoom in on New York or San Francisco.
3. Also in Layers, check the box that says "Keyhole Community BBS". When you zoom in anywhere, you can see little "info" marks that tell you interesting (or not so interesting) facts about the places you're looking at.
4. When you click on an info button, you can also click "more" to open a message board post giving more detail.
5. You can also use this message board to find more interesting locations. For instance, I wanted to find Machu Picchu, but typing "Machu Picchu" in the "Fly To" bar did not work. Instead, I search for Machu Picchu on the keyhole message board. I find a post that's useful, and it has a link on top that says "Open this placemark." Click there, and you jump to the right spot on the map.
6. The altitude is represented in 3D on the map. You can see this if you click on "Colorado River View" (of the grand canyon) or "Mount Saint Helens". Once you are close, you can tilt and rotate around your landmark using the interface on the bottom. I used this feature to look up the cliffs in La Jolla where I used to climb down to get to the beach.
7. If you are near the area where you want to find something, you don't have to retype the city and state. You can type an address or a business name. While looking at San Diego, I typed "Cheese Shop" to find a little sandwich spot where I used to eat lunch almost every workday.
8. Take a virtual trip across the US! Click "Directions" on the upper left. Type a starting destination and an ending destination. Then once the path is found, you can double-click on each waypoint. Your point of view will zoom to the location where you clicked, and you will be facing in the direction of the next leg of your journey. You can jump from spot to spot until you reach the end.