3D GraphinaBox. 
from House Of 3D .com 

This 3D graph shows graphs of selected mathematical functions in 3D. It is more of a tour than a tool. All functions have had boundaries and constants preset, to maximize your viewing enjoyment. It is an extension of my 3d wireframe applet. Drag your mouse over the graph to rotate it! This spinnable graph is designed to be fun, even if you can't read mathematical equations. Just pick some gobble*de^gook at random from one of the 'functions' menus to the right, and then look at the pretty picture  it is a 3dimensional graph of the function you chose.
The X, Y, and Z axes are where they are for illustration purposes only. Mathematicians would switch the Y and Z axes with eachother. Computer graphics people would have at least one of the axes pointing in the other direction, away from you. I wanted a set of axes that conformed to computer style axes (it is a computer program, after all), but allowed the user to see all 3 of the directional arrows (Standard in mathematical illustrations) when looking at the 'front' of the model. As mentioned above, all of these equations have preselected boundaries and constants, so you don't have to spend 5 minutes fiddling around to get a good fit and see how cool the equation is capable of looking in 3D. Some of the functions may seem backwards, but they simply have a negative constant somewhere, to make them look prettier. If you know of a really cool 3D function that you would like to send to me, I could add it here and put it up as the 3D equation graph of the month. Visit the 3D curve equation of the month. S t e r e o s c o p i c ViewMaster T r i b u t e ! 3D Fractal generator. Updated December 6, 1997 