Spotted via Phil Bradley,
Virtual Earth and Google Maps, side-by-side lets you see the same area's satellite view
in Google Maps and MSN's Virtual Earth service. Slick!
Postscript (from Gary): I've found that copying and pasting a url works best. Otherwise, you'll need to be very specific when entering an address of a location. For example, entering only a city name doesn't appear to work.
Also, this tool doesn't allow you to see how far you can zoom-in to a location. Althought this varies from address to address and from service to service, I've noticed that for many of the locations I've searched for, Virtual Earth offers a "closer" look.