Bullitt. Hands down. Although IMO, Ronin is a VERY close second.
Some others not mentioned:
To Live and Die in LA
Dirty Mary Crazy Larry
Vanishing Point
Gone in 60 Seconds (1974 version)--come on, ANY 40-minute car chase scene belongs on the list
The Transporter
All 3 Bourne movies
And if you're going to use the Blues Brothers, use the car chase scene in the mall, not the one in downtown Chicago.