This came up on the Chatterbox recently as a point of conversation. There are many options but depending upon your criteria, they may not all be good solutions.

GD is good if you want to make exportable images directly from Perl. The downside is that getting and installing GD can be difficult - particularly if you desire TrueType Font support (libfreetype). GD::Graph does make using plots easier as was already mentioned.

Tk is good for real-time viewing of charts, which is something I do for my employer, but it is abysmal for trying to save images in an exportable format.

For most things I find myself simply creating a datafile that can be read in by gnuplot. This provides a simple interface for creating graphs without making your Perl code too complicated. Of course gnuplot makes use of libgd so you need that installed anyway.

Good luck,
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