If you want to be able to do automated real-time credit card processing on your web site, we strongly recommend that you go with AuthorizeNet - they are the largest, have the best support, have been around a long time, and have a huge base of satisfied customers. Going with them will cause you the least aggravation and be the best value.
If you already have a merchant account, AuthorizeNet interfaces to a large number of transaction processing networks and can probably avoid the need to change your merchant account service provider. If you do not have a merchant account presently, they offer a package that bundles both services inexpensively.
When you apply through us, you get a substantial discount off their general rates:
Check out AuthorizeNet's suite of services, then click one of the links below to get an application.
There is also an extensive online manual available.
http://hostings.com 888-404-HOST (toll-free US/PR/VI/GU), 706-897-4743