In Modern Principles Tyler and I explain the Solow model of economic growth and show how the model can easily be run using Excel. I have also written a fun Mathematica demonstration of the Solow model.
You can see a quick animation of what the demonstration does by clicking "watch web preview" at the link above but anyone can also run the demo interactively by downloading a free copy of Mathematica Player. The Player is actually a stripped down version of Mathematica so what you see in the demo is not an animation but a computation of the equilibrium on the fly. Many of the other demonstrations in science, math, economics and other fields are also of interest.