OpenOffice Calc (the spreadsheet) can be used for this; there is a pretty good built-in diagram wizard, where you can choose what parts of your spreadsheet to chart, and how to chart them. It does good line, pie, bar, volume, and all sorts of other graphs I don't even understand, and is pretty easy to use once you understand how to feed it data. The chart stays updated with data changes, too, so you don't need to re-generate the chart whenever the data changes.
