A buddy of mine has been hard at work putting together a kit for engineers interested in getting into FPGA for the last couple of years. The essence of the product is a daughterboard for BeagleBone / Raspberry Pi / etc., which provides a Spartan 6 that can be programmed and controlled by a user app running on the Linux-based host.
Once upon a time not too long ago, he and I were discussing Bitcoin. He came to the conclusion that a functioning Bitcoin miner would be a great proof-of-concept / test app for his product.
Fast forward to today, here it is...
http://valentfx.com/logi-blog/item/fpga-logi-family-bitcoin-mining-application
As I understand it, it's probably nowhere near as fast as a comparable FPGA miner on the market.
As I understand it, they have barely scraped together the mining app from what they could find online, and there's probably a lot of room for improvement.
On the other hand, as I understand it, the device will still have market value as an FPGA playground even after FPGA mining becomes economically infeasible. On the other hand, dedicated FPGA mining appliances, I would have to assume, would be mostly garbage once their operating cost exceeds their expected bitcoin output.
Disclaimer: I haven't mined in a while, have never FPGA mined, apologies in advance if I've misunderstood or misrepresented anything!