I've been working on a uniform payments system similar to Active Merchant for the past few months. So far I've integrated Authorize.net, PayPal Payments Pro, and and Psigate. Basically you use one set of method calls, one set of parameters for making requests, and you get one set of responses.
I've spent the past 5 hours looking for the next gateway to integrate. Braintree has a great API, but unfortunately they lock you into using the SDK and don't just give you the basic API documentation so you can write your own code.
I looked at Barclays, Ogone, Realex, and a few others, but unfortunately many of them don't have public api access (Barclays), have it but don't give you a key immediately (Realex), or have it but the signup process is broken (Ogone).
I'm hoping to cherry pick a few gateways to integrate with who offer something at least half as developer friendly as CampaignMonitor offers with their v3 REST api:
http://www.campaignmonitor.com/api/getting-started/
Can anyone recommend payment gateways that respect the fact that I'm a developer and just want to integrate open source software with them, and shouldn't have to go through a ton of bull shit to do it?
I don't care what country / currency - I'm just looking for developer friendly solutions that will allow me to start writing code today.
You could have a look at http://www.beanstream.com - based in Canada. They support CAD, USD, etc.
I've played a little with their API, but havent done any significant development with it.
I do remember seeing an API wrapper package (maybe in .net or classic asp, I cant remember).
good luck.