Can’t afford a ti-89? Get a free graphing calculator with Google. That’s right. Google is now a free graphing calculator.
You can display multiple functions on one graph. Hovering the mouse over the graph will give you the trace and display the x and y coordinates. The navigation is the same as Google Maps. You can zoom in, zoom out, and pan.
Google can also graph a two variable function, and display graph in 3D. It displays a cool animation of the graph spinning around in 3D. Again you can zoom in, zoom out, and pan. This feature requires that your web browser supports WebGL, which it probably does.
Some Other Features on Google Calculator
Google has pre-programmed formulas for most common geometric objects. Plug in the value for each field to get the solution.
Check out the support page for more info.