Installed some great outlets by Leviton, model number 5844. 110 and 220 volt, 20-amp outlets in one standard duplex outlet. 220-volt equipment starts up smoother, but I'm not 100% sure where everything is going to be located. So I am installing these every four feet or so along the perimeter of the shop and at each overhead drop.
I've run four wires down the conduit to pass through each of these: ground, neutral, hot #1, hot #2. I decided to alternate which hot each 110v side of the outlet uses on every other outlet. To tell them apart I'm using the brown color outlet (5844) for every outlet where the 110v outlet uses hot #1 and the ivory color outlet (5844-I) where the 110v outlet uses hot #2. It's doubtful I'll ever run more than one tool at a time but you never know.