Frank Gruber at TechCrunch posts an excellent and detailed review of the mapping services available, covering Google Maps, Windows Live (aka MSN) Local Maps, Yahoo Maps, Ask.com Maps, and the venerable Mapquest (but not A9 Maps).
I agree with Frank that the brand spankin' new Yahoo Maps Beta, with its fast and spiffy Flash interface, is the best of the lot. If you haven't tried it, you should. It's clean, easy to use, speedy, and has some nice extra features. It's also convenient that, unlike Google Maps, Yahoo Maps Beta covers international destinations.
My only issue with Yahoo Maps Beta is that it is not yet the default on Yahoo, so I usually end up using Google Maps. I'm just too lazy to manually go to the special Yahoo Maps Beta site. Darn lazy users. I hope Yahoo moves the new interface out of beta soon so everyone can benefit.
[via Barry Schwartz]
Update: Eight days later, Google Maps launches for several countries in Europe. The satellite view of the Eiffel Tower is jaw-dropping.