I don't have a good book on optimal control, and I should get one. I have a good book on robust control which I suspect comes at the subject from a very different direction from normal, it is "Robust Control, The Parametric Approach" by Bhattacharyya, Chapellat & Keel.
It's heavy on theory, but they spend a lot of time extending frequency- domain approaches to formal robust control theory, and I've spent a lot of time using frequency-domain approaches in my work. I've done projects with it propped up next to my computer screen and had good success.
Beware of "optimal control" that doesn't mention robustness, though -- you'll get "optimal control" of a nonexistant plant, and lousy control of what you actually have (which is the whole point of robust control theory, by the by).
All in all, though, if you take a big pot, brown the traditional control methods on all sides and simmer well with a couple of quarts of experience, you'll make a better soup than you can get by heating up a can of optimal robust control fresh from the supermarket.
When I was about to start my master's degree program I inquired about getting a PhD in control theory (this was at WPI, which is good but small). I was sent to the mathematics department. While I was a grad student there I was a teaching assistant (twice!) for a 3rd-year control systems class that was taught by a biomechanical engineer and a mechanical engineer, through the ME department.
Most recently, as part of a contract I helped to hire a woman who got her bachelor's degree in economics, during which she took her first course in control theory through _that_ department, then emigrated to the United States and finished up with a PhD in mathematics -- specializing in control theory -- here in the states.
So control theory is a discipline that finds a lot of homes. If endocrinologists can't take a control theory class as part of medical school they should be able to, and if I found out that there was a school of archeology out there that required controls to graduate I would be amused, but not amazed.