Ask stripe.com for a beta invite. I recently implemented their billing solution quickfast. 3.5% + $0.30 on each transaction, but no need for a merchant account. Get in contact via http://twitter.com/#!/stripe
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.
I'd recommend starting out with one of the major "easy-to-get-started" providers like Paypal or 2co and then switch to a merchant account once the volume of sales make it worthwhile.