John advice is right. Credit scores can be overlooked if you offer to prepay your rent or add on additional security deposits. It still will depend on the landlord on a case by case basis. If you are working with an agent, have them tell the agent up front so that you are not spinning your wheels.
Extra deposit means you will still have to keep paying monthly rent and the landlord has the assurance that if you falter, they have a big deposit to back up the time necessary to pursue eviction.
Plus, its always a little more difficult to get landlord response for issues when advance rent is paid ;-)
You can work with a broker or leasing agent or do this on your own. You will need to find a private landlord for the most part. Property management companies have strict guidelines that must apply to every applicant equally.
First, hopefully you have a good reason your credit is very bad. Be very honest and upfront with any landlords property you are looking at, or, if you are working with a broker or leasing agent be honest with them. Look for "For Rent Signs" by private landlords. You can also do reverse prospecting on craigslist which is very effective. If you don' know how to do this feel free to email me and I will be happy to step you through. firstname.lastname@example.org put it the subject "reverse prospecting".