One of these!
Build your own bicycle camera mount
Has anyone tried this? It looks so cheap and simple to do - a couple of bolts, washers and nuts, an old light mount and a digital camera you wouldn't cry over if it got damaged. I know what I'm doing in the garage on Boxing Day.
And of course, the end results would be both fun and productive. On a dry day it could make patrolling the cycleways and byeways of Edinburgh and capturing "evidence" so much easier.
Of course, must be careful not to get distracted by buttons in traffic...