Depending on the area of software development then trigonometry, geometry, linear algebra, number theory, combinatorics and probability theory are the most obviously useful. Beyond that I know that there's a close relationship between category theory and functional programming. I'm not familiar with the details of that or whether it's useful in practice or more of an area of theoretical study. I'm sure there's others on HN that know though. Interestingly I used a fair amount of category theory in algebraic topology, but never closed the loop and learned much about the relationship to programming.