My camera of choice is Flea3 from PointGrey, superb image quality, speed, control settings, it does have standard C/CS mounts, you have higher choice of optics than what you might ever need.
However, for tracking people, I would use Kinect, thou range of 10 is probably too much. 7-8m is max. I do not prefer 2D image tracking since it’s never very robust and you have to consider many factors.
@mindthegap not sure about your budget, time constrains, robustness requirements, maybe you can go with ps3 eye, which is has a status of affordable and highly hackable camera for computer vision, there are lot of experiments with custom optics too. in the age of 3d printing, i can imagine it might be possible to create custom mount for more standard lenses.
…or kinect again, its ir camera does have unparalleled performance in that price category. 30fps, out-of-box IR, no bayer filter, high dynamic range which makes it much easier to do the pre-process of the image before you send it to the tracker.