Surprised nobody has mentioned the Yakima roof rack, which is affordable and very easy to install and remove. Total retail: $265 for the racks plus whatever bike mount you choose, from $60-$179 per bike. The rack mounts entirely on the tridion cell and is very sturdy. We've carried around 100 lbs up there more than once.
Great thing about the Yakima system is the wide range of accessories available for it, allowing you to carry almost anything on your car.
Search this site for "smart camping trip" to see the racks, a basket case and a farout bag in use.