I got one more class to take to complete my minor.

I've currently done Differential Equations.

So...the options I am looking at now, and have some interest in...

Real Analysis.
Numerical Analysis
Matrix Theory

Graph Theory.

Differential Equations 2

Math Modeling

Vector Calculus (Requires Multivariable calculus. I might be able to do that during the summer)

Vector calc is nice if you want to be able to derive physics constraints on-paper yourself. Matrix theory could be pretty cool for implementing higher-order math algorithms, like big matrix solving/factorization stuff. Numerical analysis also looks very fun and useful, iterative numeric algorithms are all the rage ;) The rest sound pretty boring and not that useful (not sure though! just my opinion at a quick glance).

The last three topics are more adaptable to *game* physics. I'd master differential equations (and take vector calculus during the summer) because I would be in the rhythm of the last class.

*sigh* the option is hard. Though I can see the need for mastering Differential Equations.

Here's a very good list of (intuitive) game physics topics in which you can apply some of the classes you've mentioned: http://box2d.org/downloads/. Maybe you should see what topic interests you most and stay with the class that is mostly related to it. It also really depends of what you'd like to do as a programmer if that is what you really want to become. For example, if you're interested in graphics programming (not graphics researching) then you should be fine with a solid understanding of linear algebra, most of the time involving vector and matrix manipulation, assumming you know how to implement those things.