Hydraulic disc brakes and road shifters I want to build a road/cyclocross bike with a Dura Ace 9000 rear derailleur and a matching shifter (Dura Ace 9000), but I really want to have disc brakes as well. My understanding is that a mechanical disc brake will work fine with any shifter, since it uses the same kind of cable as a V-brake, but I haven't been able to find any information about whether I can use whatever shifter I want with hydraulic disc brakes. Do I need a special kind of shifter or lever for a hydraulic disc brake on a road bike?

Update: as the answers pointed out, I do need special brifters (thanks for clarifying the term; it made googling easier and more accurate). The compatible brifters are indeed very rare and so far I've noticed that they only come as part of an entire groupset, i.e. I haven't been able to find standalone hydraulic brifters; I can, however, order a complete Shimano 105 or Ultegra groupset with hydraulic brakes (sans rotor) and brifters from certain online retailers. Secondly, what I suspected turned out to be true - Dura Ace 9000 isn't offered with hydraulic disc brakes out of the box.
You need a hydraulic shifter to use a normal hydraulic disc caliper as there is a piston that moves fluid which a mechanical shifter will not have. 

There are mechanical to hydraulic systems where the cable from a regular shifter actuates a hydraulic system on the caliper itself. They are usually a little more bulky looking. This would probably be your best option if you can't get hydraulic brifters but must have hydraulic calipers. 

You can however use your mechanical shifters with cable pull disc calipers as you noted. This works well. You don't have the hydraulic advantage of nearly zero friction in the system. You don't get that with cable to hydraulic either but you may or may not get better modulation with a cable to hydraulic.