Look into getting a dash cam with parking mode and a rear cam (often called 'dual channel'). Mine paid for itself when some moron wasn't paying attention, merged in behind me and love tapped me while we were waiting at a light. Pulled over into a side street because I hate it when people just get out in the middle of a busy main road to exchange info, looked behind me to see he wasn't even there...he drove off.
Rear 720p camera caught his plate nice and clear, the funniest bit of it was the way he stuck his hand out over the dash in an "oh **** i'm so sorry" gesture then immediately balling it into a fist and shaking it as if to say "YOU SHOULDN'T HAVE DONE THAT!"
Anyway, made a claim with my insurer and gave them the video. About three months later I get an email saying my claim payment had been refunded. It didn't actually leave any damage aside from very minor paint transfer so I never bothered fixing it up, but I like to imagine that that guy's premiums shot through the roof for a while.
If you don't mind it recording audio, leave it on and get into the habit of reading out plate numbers, especially at night - cameras already suck at recording night time video, add to this movement from driving, glare from headlights etc. and it's nigh impossible to get plate numbers unless you get incredibly lucky and conditions are perfect. The microphone still picks up audio just fine however...