Looking for partner for credit cards

Hi, I'm sure lot's of you have done their shop with PHP in the US. Could anybody give me a tip on a good partner that fits into a shopping site? I've to overwork a shop, which cooperates with paypal. They require registration of the credit card user, which is absolutely not acceptable. The shop is still very small so I'd prefer something with a very small monthly fee. Charge for actual transaction doesn't matter that much. 'Hope some of you know one or two good credit card partners (for the usuall credit cards used in the US) thx Jan