I like this one because it will work with fenders and front racks. It holds the bike by the top tube and the wheel base is easily adjusted.
http://www.performancebike.com/bikes...1_20000_400019
If I was making one from scratch I'd make the vertical stay fold down so you could open the tailgate. I drive a 4Runner with drop and a Previa with a hatch gate and that would let me leave it on and still get into the back.