I took a class called "Modern Algebra" during the spring of my junior year. It was an introduction to group theory. One of the assignments can be found here.
During the fall of my senior year I took a class on basic Topology.
I took a number theory class during the fall of my junior year. However, the course was oriented toward developing a proof-writing style.
During the fall of my senior year I took chaos theory. The class made a big emphasis on programming, especially in C++ and TI-Basic, a programming language developed by Texas Instruments for the TI 83/84 Graphing Calculator. At the end of the class I wrote a "Chaos Theory Program Pack" which can be downloaded here.