I'm researching recurring billing solutions for my web app. So far I have taken a look at:<p>http://www.chargify.com<p>http://www.braintreepaymentsolutions.com<p>http://www.payfacade.com<p>http://www.cheddargetter.com<p>http://www.spreedly.com<p>...and obviously Pay Pal. Any recommendations here? I am looking for something that is affordable and easy to use from a development perspective. There have been threads like this in the past but I wondered if anything new has come out since then.