I recommend Stripe as well. I am very happy with the integration process, the simplicity of the API, as well as their exceptional customer service.

There have been times during all random hours of the day and night when I have had a question and they have always gotten back to me promptly.

I triggered an error on their website one day and received an e-mail from them about 10 minutes later telling me a work around to avoid the problem and letting me know that they were in the process of pushing out a fix. A short time later I received another e-mail saying the fix was in place.