Verisign's Payflow Pro (http://www.verisign.com/products-services/payment-processing/online-payment/payflow-pro/index.html) is a scalable, fully-integrated online payment processing solution, that meets the large transaction demands of your online business. It gives you direct control over how your user interacts with payment functionality on your site.
Some of the useful links are listed below -
Signup for a Merchant Account: https://payments.verisign.com/SophiaServlet?FORM_FILE=vps/reg/initial.fdf&partner=&token_flag=&mode=buy
Login to Verisign's Payflow Pro: https://payments.verisign.com/register?VHTML_FILE=vps/reg/login.xsl
Knowledge Base: http://www.verisign.com/products-services/payment-processing/online-payment/payflow-pro/faq.html
Verisign's Payflow Pro Pricing: http://www.verisign.com/products-services/payment-processing/accept-credit-card-pricing.html
