Mapnificent is a Google Maps mashup that shows how far you can travel on public transport for any given time period in Berlin.
To use the map just click on a location in Berlin, set the length of time and the map will add a layer to the map showing the areas that you can travel to in that time from your location. It is possible to select a journey with just public transport or with a bike and public transport.
This map is a great resource for anyone in Berlin who is looking to buy a property and wants to work out the areas within a set commuting time from their work place.
The developers of Mapnificent say it is inspired by Mapumental, which has been in private beta for an age. Mapumental itself is trying to recreate something like Where Can I Live? which shows London property (from Nestoria) based on the public transport travel times from a given location.