Tagging Users?

Can anyone suggest a way to tag users? I’m setting up a website for a University department in which we will tag courses, projects, and hopefully faculty members with subject-related tags. It’d be nice if faculty could tag themselves when they edit their profiles, using the same tags. Any idea how I might go about doing this? I can do a little ad hoc coding but would much rather rely on someone else’s plugins if I can. Thanks,
Matt