BTW - Stripe has recurring billing and the ability to create add-ons for the monthly bills, via API.
They don't charge anything extra for these features beyond the normal credit card processing fees.
-Avi

On Mon, May 20, 2013 at 4:54 PM, Cal Leeming [Simplicity Media Ltd] <cal.leeming@simplicitymedialtd.co.uk> wrote:
Take a look at chargify.com - they are extremely good.

Cal