Cryptography is a big one. You can find tons of articles on it, although I am guessing "senior paper" refers to senior year of high school, so most of those articles will be beyond what you have studied. Here is one that utilizes a concept in number theory (the primary domain of cryptography) called Lambda Calculus:
http://www.seas.upenn.edu/~sweirich/types/archive/1999-2003/msg00480.html
Lambda Calculus, in extremely vulgar terms, is simply a method for dealing with functions that are able to return other functions instead of numbers, so you can collapse an arbitrary number of contingencies into a single-variable input. You can see why this is really useful for encryption, as well as for logic/decision theory.
Speaking of which, decision theory/game theory is another great application of calculus. Many times, we are interested in the optimal strategy not for a single move, but for an infinitely iterated number of moves. The theory of limits (which I'm sure you
have covered) allows us to do that. A great example is Bayes's Theorem, which is used to calculate probabilities contingent on one another. For example, a farm has
n turkeys and
m chickens, all turkeys are brown, 10% of chickens are brown and 90% white, and you see me carrying a brown bird. What are the odds it is a chicken? This simple example can be solved with algebra, but the underlying proof results in a system that, through calculus, can produce optimal decisions for enormously, even arbitrarily complex probability systems.
Another example within game theory is Arrow's Theorem and the surrounding literature. It's an area that deals with the design of voting systems. Arrow's Theorem shows that no voting system can be both representative and fair. Ways of getting the closest system to actual fairness and representation (including the proof that the majority rule, which America uses, is a very good one) often include use of calculus for optimization or vector operations. Similarly, Duverger's Law (all systems with one legislator per district, one vote per person, and majority rule, such as America, will inevitably have exactly two parties) can be proved with calculus-based game theory. There are TONS of journal articles about that.