It sounds like you want something like Worldpay or even Google Checkout. But it all depends what your turnover is, because these sorts of providers (who host the payment page themselves), tend to take a percentage of every transaction, rather than a fixed monthly fee that you can get from elsewhere.
The other thing to consider is, if you have any way of taking orders over the phone, and the phone operators need to take customers' credit card details, then your whole internal network will need to be PCI compliant, too.
If you JUST need it for a website, then that makes it easier. If you have a low turnover, then check out the sites mentioned above. If you have a high turnover, then it may work out more cost effective in the long run to get PCI-DSS certified and still keep control of credit card transactions in-house, giving you more flexibility, and cheaper transaction costs.
