London Buses manage to reach the corners of the city that
the underground and overland trains don't.  Cost is £1 traveling
through stage 1 (central city) - or 70p per stage from outside stage 1.

Remember that your tube passes of a day or longer, are valid for travel on buses within the
zone areas specified.  

Whilst Buses in the city tend to be fairly regular during rush hour periods, the Bus service in
the suburban areas is not noted for it's punctuality.  Sometimes, however, waiting ten minutes
for a bus may be preferable to being sandwiched under a fellow traveller's armpit on the often
overcrowded tube or train - particular during the rush hour periods.

Tips

You are allowed to jump on an old style double decker bus at any time.  This is the type of bus with
the open platform at the rear - jumping on while the bus moving at speed however, is not advisable!  
Bus inspectors are regularly found traveling on buses both in the city and suburban areas - so make
sure you have a ticket valid for the zone you are traveling through or incur an on-the-spot fine of £5.