This AppleScript will add a "Google Map Of" option to the Address contextual menu in the Address Book application. It will open Firefox and map out the address on the new maps.google.com mapping service. Note that Firefox *must* be installed for this to work.
To install the script, just save it to a file named "Google Map Of.scpt" and put it in your ~/Library/Address Book Plug-Ins/ directory. Re-launch Address Book, then control-click on a U.S. address and select 'Google Map Of (Firefox)' from the pop-up menu.
[robg adds: This script worked as described for me. Firefox is required because Google Maps does not yet support Safari. Google Maps are also USA-only (for now?), so this only works for addresses in the states. If you haven't tested Google Maps yet, it's worth the time. As you can see in the image at right, they have a fairly impressive display, and the user interface is quite nice -- especially for a browser-based application, whose UIs I typically hate.
I also received a second Google Maps script, at nearly the same time, submitted by miked378. I tested it, too, and it works as well as the first. Feel free to use whichever you prefer; I've added the notes from miked378's submission as comments in his script...]

