I did not have a hitch on my CRV, and looked into many options including a roof rack and having a hitch installed on my car. What I found to be best was the Thule Spare Me rack and have been very pleased with it. This model is adjustable to compensate for whether the spare tire is mounted on the left, center, or right.
http://www.thuleracks.com/thule/product.asp?dept_id=22&sku=963
I would not get the racks that clip to the tire itself, but the ones that connect to the spare tire mount and can compensate for the position of the spare tire are a good option if you are only going to carry one or two bikes. If you need to carry three or four bikes, then the best option is to have a hitch installed.