Paypal is certainly not your only option but my suggestion, depending on your timeline, is to use paypal. Not only is it the easiest, quickest way for you to implement your payment system, it's also a "trusted" way of payment for customers. My experience is customers are more comfortable paying through paypal for the same product vs. entering their credit card information on a "random" site they are visiting. They don't know you well enough to trust you. They know paypal though.
I've never done it but I would think in order for the CC to be processed in the background immediately, you'd have to work with the company in which you're a registered merchant. They probably have some tips and tools for you to use.
Good luck. And if you find that it's easier than I thought, let me know. I may be asking for your help. ;-)
I recommend Paypal for your requirement. Subscription kind of stuff mainly people rely on Paypal. You can test using your Sandbox account. From the IPIN you will get the responses. So get in track of things which very essential when you deal with money. Customization will take more time. Paypal forums will help you to clarify your doubts.
It's something about PayPal I feel makes a business look amateurish, but I guess it does the job. I think the PRO you're allowed to fully integrate it into your site I have to check that out.
AMAZON has a new one I tested and its very clean. They're checkout process is really quick and easy.They're trying hard to woo in customers since they're spanking new. I would use it over PayPal if there was more support.
They just don't have enough sample code for me. They dont even have code in ASP. God knows when they'll get to Coldfusion.