Yakima's HighRoller Bike Mount is a favorite around here, and for good reason. It's a dead simple design that doesn't require wheel removal, and we haven't lost a bike out of one yet. Better yet, when you're not using it, the whole thing stows flat, so your car plus rack profile isn't much higher than normal. It won't carry recumbents or tandems, but just about everything else will fit. It'll take lock cores from Yakima, which are sold separately, so that you can better secure your precious rides. It mounts easily on square or round bars.