I can advise a couple of good guide services, but at the same time, if you are looking to make a combination hunt there is plenty of good land that can be hunted for free as well. Some of the greatest waterfowling areas have really pretty good pheasant hunting as well. Not the realm of the "Golden Triangle" in the center of the state, but if you are willing to take more than an hour to take your limit, it can be very productive.
Here is a comprehensive list of hunting guides in So. Dak. http://www.huntingsociety.org/SDak.html
There are several that are more famous than others, Big Bend Ranch and Big Spur Lodge are nationally famous, for instance. Glacial Lakes Guide Service is a smaller outfit that treats a guy well but is not well known. In my area, the North East corner of the state, a great place for waterfowl and the pheasants have made a tremendous comeback in recent years, Prairie Sky Ranch provides guided hunts for waterfowl and pheasants and has been the subject of at least one televised waterfowl hunt.
For all of that though, a great hunt can be had in this area (Roberts/Marshall counties) without need of a guide, for pheasants or waterfowl. Heck, drop me a line and you are welcome to hunt with me. I am no guide and don't pretend to be, but I can give you a good idea of where the birds are in my area. There are still a fair number of farmers in the area willing to let a guy hunt who is polite and treats the property with respect.
"If you don't think too good ... Don't think too much." Ted Williams