I’m currently working with four other students on a Rails project for the ASE (Advanced Software Engineering) course at my university, which happens to involve payment processing.

We’re still in the elaboration phase and have only started to look into different solutions, like PayPal, Google Checkout, Authorize.net, etc.

So it came in quite handy that I stumbled upon a discussion at Y Combinator which gives some insights from people who faced similar questions: What is the best credit card processing setup for startups?