A fascinating stochastic algorithm for rendering some truly breathtaking fractals (there's quite a bit of more detailed info on the web page, as well as links to other people's descriptions of this algorithm). It is an iterated function system (IFS), but can be used much more easily than many of the IFS programs I've seen.
Plot3D A Math Function Plotter for Windows 95 which creates flat or 3D plots of functions containing up to 3 variables.
Equation Grapher with Regression Analyzer A program for plotting and analyzing functions. Once you have plotted a function, Equation Grapher automatically finds roots, maximum/minimum values, intersections, and so on.
Caos Graph An equation grapher. Built-in project manager for drawing multiple graphs. Calculate and display integrals. Calculate curve angles. Find X-values from Y values. Built-in calculator.