I'm on my second Saris Cycle-On (somebody hit the first one). It's hitch-mounted and works great.
We love this rack and use it a couple times a week.
* no need to remove wheels from bikes
* easily locks up with cable lock
* very well made
* doesn't touch the bike frame (my wife's particular about her aluminum road bike and doesn't want anything clamping on the tubes).
* works for both mountain and road bikes
* on and off real quick and easy
* hitch mount on the minivan is very low and morons will run into it in the parking lot!
* hurts like a b!tch when you forget what vehicle it's on and walk into it in the dark!
Cheapest I found was at www.airbomb.com