Crazy bump uses a simple and intuitive layout, and a nice real time 3d view port with enough options to get what you want, and a relatively large documentation.
It will however weigh in on your wallet at the cost of 50-300$, and 99$ for personal use. Or you can just try it for 30 days.
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Pro Intuitive interface
Almost anyone that has some knowledge on bump maps, can use this software, just dump in your image, adjust a few sliders, and export your maps.
It's a nice software, but you are going to have to dump 50 to 100$ dollars on it. However, you can give it a free go for thirty days.