It may be the coolest Google thing yet! (Well, everyone I know thinks it's cool!)
The site changes all the time and new tools and views are constantly being added. When they first started only North America was covered (but not including Mexico, unfortunately). Now (Spring 2006), most of the UK is covered, northern Italy (I guess they did that part for the Torino Olympics) and Japan seems to be all included, although that part is in Japanese.
Also useful is the Hybrid view which combines the Satellite view with street names from the Map.
Go to: Google maps
From the starting point, you can zoom-in on anywhere that you want to see.
Just type-in the location in the search bar. The rest is obvious. You can navigate east-west-north-south with the arrow buttons on the left and zoom-in or zoom-out using the slider.
And now, use the Satellite link on the right to get a satellite picture of the area you're looking at.
Told you it was cool!