Henry Ford was an obsessive collector--the museum has everything from cars to steam engines to early electronics to household gadgets from 100 years ago to airplanes. The place is absolutely amazing and takes a minimum of a full day to see, not even counting the village itself, which takes at least another day.
Probably the best old car museum is Gilmore Car Museum in Hickory Corners, Michigan.
+1 on that. The Gilmore has more old cars than you'd believe, including the oldest car known, steam powered cars, muscle cars, the biggest collection of Lincolns you ever saw, and more. Many are on loan from other collections.
The best time to hit the Gilmore is on the summer weekends when they have car shows where a few hundred private owners bring their personal vehicles, park them in a huge field, and everyone sits around in lawn chairs while spectators wander around looking at the amazing variety of antiques and hot rods. If you like old cars, hot rods, and muscle cars, it's not to be missed.