A
Saris Bones RS Trunk Rack is a great option, as is the
Swagman XC Hitch Rack, or even a
Thule Raceway 9002 Trunk Rack, but with so many options I highly recommend that you
read this to really drill down and find the best bike rack for your specific needs:
http://www.bestbikerackreviewsite.com/bike-rack-test/