In London the buses are free for under-18s, those over 60 and for wheelchair users. However knowing which bus to catch to get to your destination can often be tricky. Transport for London provide bus maps in PDF format but don't provide an online interactive map. Which is where What Bus? comes in.
What Bus? is a Google Maps mashup of all the London bus lines. It is possible to search the map by postcode or by just panning the map. The bus routes are shown on the map by coloured polylines. Clicking on any of the bus routes will take you to an individual route just for that line.