Do buy a travelcard so you can jump on and off ordinary buses - by far the best way of sightseeing. Helpful info at most central London bus-stops too - Ato Z listing of streets, places etc and the number of the bus needed to get there. Dead easy and when you pass somewhere that you think you'd like a closer look at, just hop off, have a look then jump on another bus. Since I've had my bus pass, I've never used the horrid Tube.