Along with all the slick widget packages--BLT, ClassyTcl, and so on--which build in canvas-oriented barcharting, there's a dead-simple but too-little-known pure-Tcl technique for generating barcharts for Web applications.
[Show picture of example output [L1 ]. Show sample code. Discuss axes and legends. Explain alternatives for generation of color image. Refer to color codes.] [Probably written up 23 April 2002.]
"Web special effects" has related information.