WEB based Customer Account Management Solutions - B2B

Hi All

Just looking to see if anyone has come across a wheel that ahs been invented - Before I ask out IT Dept. to invent a new one.

We are looking for a Web based Portal to allow a level of customer account management off the back of our existing B2B customer website and out internal Document Management System that would provide the data and documents (Statements, Invoices. Credits etc.) and would like allow customers to navigate to a payment gateway to pay selected invoices and credits of their choosing.

Is anyone aware of a 'packaged' solution to this, accepting it would need to be tailored to our data and existing website I would appreciate hearing from them.