I usually don't write about third party solutions, but this one is getting its place in my blog.
A fellow CRM blogger Wolter Kreun from the Netherlands is developing a freeware plugin (Can it be true? A free and very useful plugin for CRM!!!) that fully integrates Google Maps into Microsoft CRM. Soon it will support MS Live maps.
Haven't tried it, but as far as I have seen on the videos it ROCKS!
EDIT (05. oct. 2009): I just have been informed that the link provided below does not work anymore. But you can use similar integration with virtual earth at: http://www.crmwatcher.com/2006/11/virtual-earth-3d-maps-integration-in.html
So chop chop guys and click on this link: http://mscrmgooglemaps.blogspot.com/