Dear Shalev,
well, gnuplot maybe seems difficult if one doesn't have a cookbook such as
_http://t16web.lanl.gov/Kawano/gnuplot/index-e.html_
(http://t16web.lanl.gov/Kawano/gnuplot/index-e.html)
handy. If that still doesn't convince you of gnuplot, you could have
a look at the screenshots of MRPlot, which is pure Ruby
_http://www.harderweb.de/harderware/index.php?mod=mrplot_
(http://www.harderweb.de/harderware/index.php?mod=mrplot)
Best regards,
Axel