Google Maps

As everyone probably knows by now, Google Maps is the coolest mapping program in existence. Even better, the management has just introduced satellite imaging, which isn't that useful but makes it easy to waste hours on end. Finally, the site is written using a publicly accessible XML interface, which some people have used to add extremely useful and interesting features of their own.

Now, if only they could add a scale feature, and perhaps symbols for landmarks such as hospitals and subway stops... but even now, it's a revolutionary improvement over its competitors.