Have you ever been able to get a refund for a non-refundable ticket?

You might be able to get a credit. Southwest gives credit on future travel for 1 year on cancelations and changes to non-refundable tickets.

When you say cancellations, do you mean customer initiated or airline inititated?

Customer. I changed a ticket on Southwest once and they credited the difference. I assume this would be the same with cancellation because the way they do it is by first canceling your original ticket and then making a new reservation. I could be wrong though.

Ah, I'm working on a situation where the airline cancelled my flight reservation one month after it was purchased. They issued a paper voucher about 1 year after the incident, but it was for $100 less than the purchase price of the ticket. I just want my $ in full.

Wow. That has to be a mistake. I can't imagine why an airline would not give you your money back.