I spent a full week evaluating Amazon, PayPal, Authorize.net and a couple of smaller players (don't remember their names). I even posted a detailed report here

I spent a full week evaluating Amazon, PayPal, Authorize.net and a couple of smaller players (don't remember their names). I even posted a detailed report here somewhere in August. Authorize.net is the big daddy of online payment processing. I found it to be most developer-oriented too. Amazon suffers from unnecessary complexity and tied to their own stuff too much, besides not a single support person (on the phone) knew anything about it. PayPal was not very "customer friendly", in fact their sales people sounded like typical scammers/car salesmen and overall PayPal not as developer-friendly as authorize.net In the end I implemented everything (one-time payments, scheduled payments, etc) in just two evenings using a couple of PDF downloaded from authorize.net. By the way, another reason to use them is the dev. community. Thousands of devs built stuff for authorize, i.e. there are libraries, code samples and docs on numerous blogs for every imaginable programming language/framework.