I got a veho muvi as a present last year, absolutely great, record for about 1.5 hours , and charges from a usb port, so small you dont notice it, also 7dayshop do a cheaper version for 15 quid or there abouts, had 2 and both broke, though excellent service they where both replaced free.
Ive fitted mine to the rear skull strap of my helmet,and points backwards, it lets you see the various hand gestures, and how close some idiots come to you, never had a problem with buses though.
Buy an extra mini sd card as well for a spare, to record going home as well, they record sound, so if a car does cut you up, talk a description of the car, reg and driver and it will be recorded on the card, i also say at the begining, that its what ever time it is along with the date.