Bullitt is right up there but there are so many good chases, it's hard to choose a favorite.
Not really a chase but I love the scene in "O Brother, Where Art Thou" where a center-door T crashes through the burning barn - driven by a kid wearing a leather aviator helmet, sitting on a couple Wards catalogs, and with wood blocks strapped to his feet to reach the pedals.
Another good one in that movie is when the boys are picked up in a 33-34 Ford being chased by cops and driven by Baby-Face Nelson - who proceeds to machine-gun everything in sight...including cows along the road.
