Dunlop SP Sport 01 A/S (Ultra High Performance All-Season) 18s on mine.
At the dealership I bought mine at, the 4 doors had the Pirellis and the 2 doors had the Dunlops when they had the 18" Detroits (which most did have, I think I saw 1 car with 17" out of the 11 cars they had at the time.)
Not sure of the logic behind that. Also, interestingly, Tire Rack survey ratings were much better for the Pirellis than the Dunlops and the Pirellis cost less (mid $130's vs mid $170's per tire, go figure) Something to keep in mind at replacement time.