I have been usinng WHMCS.com's billing system for a few months. It has modules to handle many payment systems, and handles recurring billing. You still have t

I have been usinng WHMCS.com's billing system for a few months. It has modules to handle many payment systems, and handles recurring billing. You still have to have a merchant account; but, you have the potential to save 2-3% of each sale, since you will be dealing with the payment processor directly.