I consider a solid understanding of discrete math to be a necessary skill for any type of programming. If you don't agree, I submit you probably don't know discrete math very well. Learn it, and you'll be enlightened.
I've only just started delving into lambda calculus, but what I have learned so far has drastically improved my productivity and the quality of my code.
If you're interested in anything involving free motion, i.e. an Asteroids clone or an FPS, then trigonometry and linear algebra are important. A solid understanding of differential calculus can significantly enhance your understanding of many problems you might encounter with your update loop as well.