Google released “Maps Ad Unit,” a new feature that will enable geo developers to generate advertising revenue from their Google Maps API implementations. This new opt-in Maps API feature overlays AdSense ads over an embedded Google map on your site. The ads are targeted to the map's view and update as the user moves around the map. To generate revenue after adding the Maps Ad Unit to your Maps API implementation, you need to link it to an AdSense account enabled with AdSense for Content.
More info: Geo Developers Blog