Java World has a good example of how to put together an interesting Mashup involving Google Maps. I find it interesting because google maps does not have the ability to lookup positioning coordinates based on address information. However, this Mashup solves that problem by using geocoder.us to translate address information into the coordinates needed. In addition the Mashup is using DWR, which I find to be the easiest way yet to get AJAX functionality into Java based web sites.