FreePatentsOnline has launched a new patent mapping service called Local Patents. The service combines inventor and assignee city data from 3 million US patents and published applications with a map of the US generated by Google Maps.
It's very cool. You can drill down from the state level to city/town. The number of patent documents in a given geographic area is displayed in a circle ranging from purple (for high numbers) to green (for low numbers). Clicking on the city/town will list the titles of the documents granted to inventors/assignees in that location.
There a some glitches. A few patents do appear in Canadian cities, but not enough to account for all the US patents granted to Canadian residents. Some of these appear to be correct, but others are obviously wrong.