Google Earth
http://earth.google.com/
Not too long ago Google acquired Keyhole, which offered a great desktop application allowing you to see satellite imagery. Renamed Google Earth and souped up with a great set of controls and much more available imagery, this is a great free application. Whether you want to see your own neighborhood, look at an area where you are thinking of buying a home, or checking out a vaction spot, this one is just plain fun to have and use. Google Earth now allows you to search for schools, parks, restaurants and hotels. You can even get driving directions. And for some 38 cities, you can tilt and rotate the view to see 3D terrain and buildings.
