You can/do get a lot of specialist controllers for the PC, but they tend not to be as widely available as the PS2 etc ones (partly because you don't generally need them).
You can get special headsets for flight sims that allow your game to track where you are looking
You get all sorts of joysticks right up to the top of the range, replicas of the controls from fighters.
You can get various dance mats
You get assorted specialist mouse type controllers (iirc MS dabbled in them, Strategic Commander etc)
You get all sorts of specialist keyboard setups.
I'm fairly sure there are even fishing rod controllers available in Japan.
But mainly you don't need special controllers for PC games, as the keyboard/mouse (with the possible addition of a basic stick) will control almost any game, often with a much higher degree of accuracy and versitility than almost any console controller.
About the only console controller i've seen that matched (or even beat) a good keyboard/mouse/stick combo was the Steel Battalion stick for the X-box.
That was a very specialised one for 2 games, it had 2 sticks, foot pedals and a load of buttons which enabled it to give a very good control system for the games (in fact it reminded me a lot of the setup I was using 10 years ago for Mechwarrior 2).
I wish there was a way to hook it up to the PC and use it in games like MW4 with all the buttons on the controller available.