I use the Metro Vac-N-Blo Automotive Series Vacuum (Model # VNB-83BA) This powerful little sucker does a great job vacuuming as well as blowing the water out of the doors etc...

Metro Vac N'BloŽ Portable Vacuum doubles as a powerful blower. Blow dry your car or motorcycle or vacuum your vehicle's interior with one Metro Vac N

I've had this for ~ four years and it's perfect for the cars.
I think this is also available at Home Depot.