I use Paypal's recurring billing API directly. It's not an ideal solution, but being based in the UK without a merchant account it's the only one I have available. I use ActiveMerchant and some extensions to talk to the Paypal API but I've had to write the logic to handle recurring billing myself. I'm trying to extract that logic into a gem and make it more robust. I'd like to eventually release it and possibly save some headaches amoung small developers who just want to get up and running quickly.
We have also dealt with this manually. We'd love to see a more robust API out there that would integrate better with our existing payments solution as we do a mix of subs and license sales. Please post to HN if you get anything of the ground!
