It may be a sad commentary on modern society, but we fully understand why people would want to install cameras in their cars specifically to document what exactly might happen in an accident. We just don't think the ideal solution is a modelthat it could obstruct a driver's view and possibly cause the very accident it's trying to monitor--no matter what have to say about it.
Clarion's "DriveEye" may be a good compromise, though Technabob says it's available only in Japan at present for about $412. It's small enough to be mounted on the windshield without blocking the main line of sight and doesn't look like a as other models do.
As do other automotive, the DriveEye automatically starts to digitally record the action upon detecting sudden braking and, if a crash does occur, saves up to 15 seconds of video before it happens and 5 seconds after. But be careful not to confuse it for installed overhead, or you may inadvertently cause the crash you're so worried about.