What are some technologies for providing subscription services?

I am working on a service and would like to provide it for a monthly fee. I've considered accepting physical payments and then manually managing the subscription database, but that sounds shady in my opinion, and not at all scalable or practical.

What are some platforms or frameworks that help with the process of processing the actually transaction and managing this kind of thing? I've heard of Magento, but that's about the extent of my knowledge of the subject.

I really have no idea what kind 开发者_如何学Goof level of abstraction are provided for this kind of thing. The application is being developed in PHP, if that matters.

Amazon FPS

Paypal's Recurring Billing Service

chargify.com

authorize.net's Automated Recurring Billing™

I'm sure there are more if you care to Google a bit.

There's SaaSy.com for downloadable products and subscription-based services, it's all-inclusive.

Another one is http://zuora.com