We've had great success using the ACS/OPENACS ecommerce package with verisign as our processor. Cybercash was the only supported processor at the time we took this feat on, and has since been bought by Verisign (thus, the SDK was replaced as well). I modified the previous cybercash module and it has been in production for us for a few months now. You can check it out at:
Let me know of any questions.