As far as fonts go, if you have Freetype support in GD, you can (I believe) use any TrueType font in GD::Graph—depending on what degree of "nice" you're looking for, that might be sufficient to your needs. For nicer-looking lines, you might take a look at this patch on RT—it isn't included in the current version, but I am (*cough*) reliably informed that it's supposed to be in the next one, and it seems like it would solve your jaggies problem handily.