With that criteria, you will be looking at a roof rack system or a simple strap-on rear mounted system. If you don't have a hitch receiver then a hitch-mount rack option will be both most expensive and hardest to install.My criteria includes the following (most to least important):
Ease of loading and unloading
Ease of installation
I use Thule racks. I have both hitch-mount and roof racks for different vehicles (both for the Renegade). I prefer the hitch-mount for ease of loading/unloading. Go to www.thule.com or http://www.rackattack.com/ to see some of your options.