Graphing Software

[Sisyphus]

I'm looking for good, cheap (or free) software for graphing functions, at a minimum roughly on par with the capabilities of a TI-83 or something. Any suggestions?

 

Oh, and please don't say "write your own." My programming skills are limited to messing around with BASIC.

[Cap'n Refsmmat]

http://www.gnuplot.info/

(download at http://sourceforge.net/project/showfiles.php?group_id=2055)

 

It's command-line but it works fairly well. You may be able to find a GUI for it.