This is a bit of the code I was discussing earlier for refunds through Cybersource. It only works with SOAP for now so keep that in mind. You're free to modify the code, but if you do something interesting, please post it back here in the comments! :)

Download the Cybersource Refund SOAP module Here

Here's the writeup from the module file:

// A quick and dirty module for processing 
//    Cybersource SOAP refunds.
//
// Author: Greg Eisenman
// Date: 5/23/09
//

Just throwing this out there to gauge demand...we just created a module (for 98main.com) which processes refunds for Cybersource transactions created through Ubercart. We don't use the Cybersource module for Ubercart because at the time we set up the site I believe SOAP was either not integrated into that module or perhaps it didn't do specifically what we needed.