The question is answered with a question for good reason.
What do you want to do with it?
[list=][*]Record for more than 20 minutes?
[*]Record in the rain
[*]Talk to the camera/Give commentary
[*]Record in HD[/list]
etc etc
Some cameras are £100, and for 20 minutes on a trackday recording a few laps are fine, in the dry.
However if you want to record your three hour commute for insurance purposes in any weather giving commentary to the camera then you're looking at a different solution.
You obviously get what you pay for.
The pov as mentioned is good.
8 hours battery/record time with an 8 gig card.
Fully submersible
Can power it from the bike (cost more for the adapter)
Broadcast quality. (SD)
That'll run you £500 with a mount kit and carry case thrown in free (atm)
(unboxing/review video
http://www.youtube.com/watch?v=W6wfPbTraaI)
Or for eighty quid you can record a couple of hours at a time on this non waterproof device.
No external microphone input.
Battery is internal and not replaceable.
If you shop around people claim to get it for as little as £40 (it goes by different names)
http://www.youtube.com/watch?v=h7mrwerNm-4Someone said if you buy in bulk from china you can get them for £8 each! I don't know if that's true or what "bulk" is.
Good luck
Oh, I'm getting the first gopro hero camera in the country shortly, and I'll be making a unboxing/review video.
I'm selling a quad camera dvr system (4 cameras, records front/rear/face/arse for example) £400 if you're interested
again, it's broadcast quality.