I just got the Saris Bones 2 bike rack. Can't complain.
It's pretty easy to put on and take off once you fit it initially, and it collapses pretty well to just keep in your trunk.
I've only found 2 drawbacks. There's no way to really lock it to your car so if you're like me you'll be packing it up whenever you're not using it (would be seriously easy to steal). My front tire swings around on it, which can be bad when it whacks the rear bumper. The guy at the LBS told me some people can loop the stabilizing strap through the wheel to overcome this, but others need to use a bungee.
I like mine. I don't have enough need to get anything more, and I don't mind taking it off when I don't have a bike on it.