journeyplanner.com
London Bus journey planner
Like with London trains, London buses are timetabled so just turning up at a bus stop in the hope of a bus is not advisable. There are so many bus routes across the capital that it is unfeasible that you couldn't make a journey enirley by bus if you wanted to (although, you may find the journey a little slower than train of course!).
To find the details of all the London bus routes, you should visit the Transport for London website (formally known as London Transport). Also, the tfl Journey Planner caters for routes via bus as well as Tube and train. In fact, you can put in your starting London post code and end postcode and it will find out the best route to your destination using any combination of tube, train, bus and even walking!