I'm running an Ultegra 9-speed cassette with Mirage 9-speed Ergo shifters using the JTek Shiftmate. The Shiftmate doesn't really work all that well, though, so I will eventually be getting a Campy cassette, probably in the spring.
If you have the option, why not just go all Campy?
EDIT: Who are all these people successfully using Shiftmates? I have one, and, quite frankly, it sucks. The shifting is inaccurate and inconsistent. I wonder if I have a "bad" one, or something?