I like to use the flexibilty of the various canvas widgets, to make custom graphs. See Tk Realtime data aquisition or Goo::Canvas Graphing demo or SuperFormula with gnuplot and Tk for examples. It is much more labor intensive to setup, but for certain applications, it beats the graphing code that comes pre-boxed for you. Gnuplot and PGPlot are very good, if you want to learn their methods.