What is a good camera arrangement for city riding? I would like to have continuous camera coverage while commuting on city streets, in order to have evidence in any collision.  I have been experimenting with an ATC3K mounted on the pannier rack, facing backwards.  At 15 fps on a 2Gb SD card, the maximum it can use, it provides about an hour to 90 minutes of footage.  I manually stop and start it at the beginning and ending of each ride.

Pros 


The picture quality is adequate at 640x480. 
It cost about $100


Cons


The chain and freewheel clatter mask any other sounds.
The control screen is hard to see and the buttons, which are under a water-resistant rubber cover, are hard to press.  As a result, it takes about a minute of button mashing to erase the SD card.
Fairly narrow field of view.
Full coverage would need two cameras, and twice the amount of fussing, before and after each ride.


What cameras and mounting arrangements might be better?
I've had good success with the Go Pro cameras for whitewater kayaking. We generally mount them on our helmets. They stand up to quite a beating and you can get more on a card than the camera you ask about above.

If you can mount it on your helmet then it will be pointing where you look and I think you'll have better success getting shots of any collision since you're often looking at it as it happens.

Here's a blog of someone doing the same thing on his daily commute. http://cranks-on-cam.com/ Looks like he's using a Drift Inovation (http://www.driftinnovation.com/x170-action-camera.php) and there is a video of his mount on the gear page.