I'd try calling the cops, and saying that you believe your car was vandalized by the driver of another vehicle, plate # XXXXX. Only do this if your looking for a clean and legal payback, if you run the plates through them and then key his car back or just straight out pound him, theres gonna be an easy suspect. If you're just looking to kick the crap out of him (not that I reccomend or condone this, of course :nono) a number of websites offer license plate lookups for a fee.
I'd be wary of the second approach though, cause I know I'd feel pretty bad if i got the wrong guy and taught him someone else's lesson. The best route is probably to call the cops and try to get them to investigate, you might get lucky. Or they might tell you that they have real crimes to deal with instead, in which case option #2 might be your only recourse.