Card Service International is one of the most widely known credit card processing companies out there. Upon starting up a small clothing shop in my home town, I set up my merchant account with CSI. Though it was far from smooth sailing, I had an overall positive experience with the company. It was somewhat difficult to discern who to call in order to resolve various problems -- my account rep, the equipment company, or a general service number -- but once I found the right people, my questions were answered quickly and honestly. And even though my store closed before our merchant agreement was up, they gave me a discount on paying off my contract, which I really appreciated.
Some other reviews of Card Service International can be found here and here.
Based on my own experience as well as the other reviews I've seen, I have to give Card Service Intl
My searches have turned up some excellent reviews of Merchant Warehouse credit card processing services. Overall, this processor is cited as being reasonably priced, quick to set up, and accessible online and off.
Merchant Warehouse also approves 99% of the applications it receives, which makes it a good possibility for high risk merchants and newer companies who are looking for an easy start-up.
Of course, not all the reviews are positive. Here's one from a customer who was none too pleased with Merchant Warehouse.
As always, read up, do some searching, and make an educated choice before signing anything with any merchant services company.