The European Festival Map is a Google Map of all the summer's musical festivals throughout Europe.
You can use the map to find your nearest festivals. When you click on a festival's marker you can find out the dates of the festival and click through and get details about tickets and the festival line-up from ChooseFest.
Festival Searcher is another Google Maps based guide to all of the music festivals taking place this summer.
The map markers are colour-coded by month so that you can get a quick overview of what festival is taking place when. I assume the size of the markers relates to the size of the festival displayed.
Télérama has produced a Google Maps guide to festivals taking place in France this summer. As well as being able to view the locations of all the festivals on Google Maps there is a comprehensive guide with detailed previews.
It is possible to search the map by location, type of music and by date. It is also possible to get driving directions to any of the festivals and to view Street Views of locations.