I purchased GeigerGraph for Networks from Mineralab, and joined the radiation network, which is a network of volunteers all over the world with radiation monitoring stations that report local CPM (counts per minute) ratings. In the graph below, you can see my station in the East Bay in slightly darker yellow.
I can highly recommend this software. The maps show active monitoring stations all over the world, and one can obtain more detailed information for each station. The software also generates graphs or spreadsheets of measured data, and allows specifying alert actions, such as sending an email, when CPM ratings exceed a certain maximum. The software can also post a real-time map on a server.