The movie below shows the graph of the function f(x,y)=2xy/(x^2+y^2). We analyzed the discontinuity at (0,0) for this function. You can view the graph from different angles by moving the control slider at the bottom of the movie frame.
This Quicktime clip was produced using Graphing Calculator on a Mac. A demo version of this program comes installed on any new Mac. The quality of the graphics using the program itself is far superior to what gets exported in a Quicktime movie such as this.