Depends what you want to use it for :-
if you want it to record longer rides and don't want the hassle of the changing the battery - then the fly 12 is a serious contender with its 10 hours battery life.
If you want top notch quality then the go-pro range is the way to go - but battery life can be as low as 90 minutes
Garmin Virb - has slightly longer battery life around 3 hours I think.
I have the fly12 and I tend to do longer rides - I have seen it as low as £130 - average price is around £160 - good thing is that brackets/SD Card are included in the box - many of the others these aren't. It has its shortcomings but once you get to know it - it is pretty good.
Then there are the unbranded budget options, which some people get on absolutely fine with, others not so much.
Thanks for the info. I have thought about getting one after occasional incidents with idiot motorists. The latest one was a couple of weeks ago when crossing a dual carriageway via a roundabout. A car approaching from the left, appeared to be slowing down to give way to me, but then drove out in front of me. If I had been 12 inches further on, I would have hit it. It was an outrageous piece of dangerous, negligent driving. I was incandescent and for the next 20 miles as I rode home I was thinking about a camera so I could report such incidents with evidence in future.
I suppose though, that unless you have one with battery life long enough to leave on for the whole duration of your ride, it could be a matter of chance as to whether you actually capture the incident. In addition, will the police always take on an investigation of such incidents, especially in these days of seemingly everlasting austerity and cuts?
There is of course, also the fun and interest angle of recording certain parts of your ride, which was my secondary, but much lower priority, consideration for getting a camera.