I received a nice package in the mail today from K6KX containing a set of keys. The price is not cheap ($99) but they are the best feeling keys I have ever used. They come with two cables, either of which can plug into the back of the keys. One is a normal USB to USB cable. The other is USB to PS-2.
I have not connected it to a USB host yet, but I used it with my PS-2 keyer / kbd for over an hour this afternoon at 67 wpm. This is definitely at my upper end. I believe I can tell a distinct improvement in my error rate.
The key caps have excellent spacing between edges so I am less likely to accidentally hit two keys together.
The keys are mechanical using Cherry switches. They have excellent tactile feedback and plenty audible feedback.
They are available from Rosewill through Amazon.
They are also the first set of keys I have had where the output cable plugs in. No big deal, but kind of nice. The dual format (PS-2 / USB) is handy also. All of my kbds currently are PS-2, but I am working on one that uses a small embedded Linux board that will work with USB keys if it ever reaches the stage of being ready for use on the air.