Authorize is a very common one, and moneybookers is the second merchant processor in the world after paypal. As said before, if you do plug ins to your main module instead of rising the price it would be best. People would be able to choose what they need, and I'm sure you would make more money this way too....

In my case for example, I would buy the full package, but if in 2 months I got issues with alertpay and paypal, then I would buy a moneybooker addon, etc....