Undergrad:
Useful: Seminar on Exploratory Data Analysis (Tukey, pretty sure this was late undergrad but could have been grad school), Game Theory/Linear Programming (taught by John Nash’s advisor), Real Analysis (don’t remember who taught it).
Enriching: The Symphony (Levy); Social Psychology (John Darley/Joel Cooper).
Grad:
Useful and Enriching: Bayesian Inference (Don Rubin); Competitive Decision-Making (Raiffa).
All but the Symphony course were practical and useful. I was privileged to have some of these instructors.