Jimmy uses one that he has high praise for, but I can't remember the name, nor if it is available internationally, but I'm sure he will drop the link in here soon : )
Myself, I use the PayPal gateway. Yeah, yeah, I know there will be plenty here that will disagree with me, and they will all have valid reasons why. I just think if you are only turning over a moderate amount of cash, PayPal offers the best bang for your buck, but just beware that they are a law unto themselves : )