If he has MS Windows, I like this program WinPlot:

it can graph functions, 3-dim surfaces, implicit functions, differential equations, and more

It’s not as powerful as some other programs out there (that you have to pay for), but can make better graphs then a graphing calculator (in color too, and then you can print them/add them to a document). I used it to make the “proof without words” of the pythagorean theorem that’s my Y!A avatar.

Best of all, it’s free! =)

i would say Microsoft Math 2007