Mashups on Google Maps are amazing and I plan to start one as son as I get a free moment, but before I do that let me introduce you to two new mashups.
SpotCrime, is a Google Maps mashup that pin points recent criminal activity and helps customers to avoid troubled streets and neighborhoods
Crimes are depicted as small icons according to the type of incident, and users can filter crimes over a certain date range or time period. Clicking on an icon brings up more detailed information .
More details about SpotCrime are available from TechCrunch.
Another mashup that is designed to guide you through safe areas is Safe Road Maps, developed by the University of Minnesota.
With Safe Road Maps "you can enter an address and view the roads that have the highest number of traffic fatalities in a specified area." The data comes from Fatality Analysis Reporting System (FARS) created by NHTSA (the National Highway Traffic Safety Administration). Resourceshelf has more info.
And if you love mashups as I do, check this post from Mashable to see the "13 Must-See Google Maps Mashups".