Here's a photo of my car I took with a rig attached to the roof and windshield. We rolled the car slowly down a parkade with a slow shutter speed to get the motion blur.
I used 2 Manfrotto suction cups and a 15ft galvanized pole with a Manfrotto Magic Arm which the camera was attached to.
Camera used was a Canon 40D with a Canon 17-40L Lens.