I want to find a directory or list of credit card processing services
or aggregators for merchants. Preferably services that process online
credit card transactions.

Hi! Thanks for the question.

I have found the following directories of Ecommerce credit card
processing services.

?Onlineorders.net - Ecommerce Directory: Credit Card Merchant Accounts?
http://www.onlineorders.net/links/Credit_Card_Merchant_Accounts/more2.html

Business.com Directory
http://www.business.com/search/rslt_default.asp?r4=t&query=ecommerce+credit+card+processing

Yahoo: Credit Card Merchant Services
http://dir.yahoo.com/Business_and_Economy/Business_to_Business/Financial_Services/Transaction_Clearing/Credit_Card_Merchant_Services/

?Web Site Designers Directory -   Merchant Services?
http://www.1234-find-web-designers.org/merchantservices.html

?HBBO Resource Directory?
http://www.home-based-business-opportunities.com/resources/business-resources-merchant-services.shtml

?121 Merchant Account Service Directory. Accept credit cards today?
http://www.121merchantaccount.com/Directory/0-9.html


Search terms used:  
Ecommerce "credit card" processing services directory

I hope these links would help you in your research. Before rating this
answer, please ask for a clarification if you have a question or if
you would need further information.
                             
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Easterangel-ga                              
Google Answers Researcher