I mentioned in my last post, the time to think of clever things to do with your schedule is generally not your first semester. But once you get into the rhythm of things there's plenty of options.
One of these options is to select a minor. A minor is a collection of classes (generally about 6) that go beyond the classes dictated by your major. Minors are designed to give you a well-rounded glimpse into an area of study that, while interesting, is not what you want to devote your college education to.
Minors are also used to supplement your major, making you a more well-rounded <insert your major here> during college and when you begin your professional career. For example, several engineers I know are minoring in Mathematics because Math was the thing that attracted them to technical disciplines in the first place. Another new, very popular, minor is Green Engineering. This is a minor that gives the students an understanding of the way that their engineering decisions have very real impacts upon the environment and I've heard many positive things about it. Another approach to selecting a minor is to choose something totally non-technical. The College of Arts and Letters is very popular with minors, including a Pre-Law minor (which I'm currently pursuing) which can present a nice public policy dimension to an education in engineering design.
Of course, minors are not the only way to diversify (and complicate) the ritual of selecting classes.