Google Maps
Google Maps is a free, online map service provided by Google. It offers a draggable map, route planner and business locater for the U.S. and Canada. It is currently in beta testing.
Visit the site - http://maps.google.com/

Microsoft Virtual Earth
A map service that lets visitors zoom in on a local area and get information about restaurants, cafes, hotels, dry cleaners, and so on.
Visit the site - http://virtualearth.msn.com/

All I can say is that, they're both cool.
One online map service is good. More services, the better.