In Exile On Main Street, Sam drives a black 2006 SRT8 black Dodge Charger. When Dean offers him the Impala "because she should be hunting" Sam refuses, saying he has his car fitted out how he likes it.
The Charger has Illinois plates, I4Z 0892.
Dean and Sam seem to see their cars as in competition with each other, as seen in The Third Man:
Dean: Still driving the plastic piece of crap, huh?
Sam: What's your mileage, again?
Dean: Shut up.
Sam: Were you racing me?
Dean: No, I was kicking your ass.
Sam: Very mature.
The Charger was totaled after Castiel and one of Raphael's angels fell out of a window during a fight and landed on it.6.03 The Third Man