As with math, the creative field of game design doesn't intuitively seem to require a strong scientific background. But if we've already established that math is useful, science shouldn't be too much of a stretch from there.
Physics I. As I mentioned when I was there, any game that uses physics (and there are many of them) requires knowledge of kinematics. Taking the rest of the sequence (heat, fluids, electromagnetism) is not necessary, as those aren’t used in games nearly as much.
Biology I and Chemistry I. Some aspects of game design are scientific in nature (consider that an advanced prototype that asks the question “is this particular mechanic fun?” is essentially a scientific experiment), so a basic understanding of the scientific method is useful. A good basic Biology and Chemistry class will teach you about the basis and methods of science. A bad class will just make you memorize a bunch of stuff and not tell you why it’s useful at all, but at least it gives you the opportunity to meet some Bio/Chem majors who can explain it to you if you ask. Your best bet is probably an intro course for non-majors, if one is offered at your school.