I drive a Jeep Wrangler, so I use a spare tire rack. It rides high on the spare so the bike wheels are about the same level as the bumper.

I strap my wheels to the forks with velcro straps to prevent spinning. The Wrangler is a pretty rough ride, but the bike is very stable on this rack.

Allen makes all kinds. Here's the website:
http://www.allenracks.com/

Good luck!