I took differential calculus during the summer before my junior year.
I took integral calculus during the fall semester of my junior year. While studying techniques of integration I stumbled upon an interesting integral. The solution was published in LSMSA's Folio magazine (2011). You can see it here.
In the spring of my junior year I took multivariable calculus. However, the class went very slowly and not many topics were covered. On my own I learned the topics skipped in class. On of the assignments in the conic sections chapter involved deriving equations for an ellipse and a hyperbola from the basic definition. It can be found here.
In the spring of my senior year I took an interesting class. It was called "Applied Vector Calculus" and was taught by a physics teacher. It covered the fundamentals of vector calculus with an emphasis on their applications in physics. The class involved a project on electricity for which I had to write an interesting C++ program. Details can be found here.