ChartDirector
http://www.advsofteng.com/cdphp.html
GraPHPite
http://graphpite.sourceforge.net/
JpGraph
http://www.aditus.nu/jpgraph/
LibChart
http://naku.dohcrew.com/libchart/pages/introduction/
pChart
http://pchart.sourceforge.net/
TeeChart
http://www.steema.com/products/teechart/overview.html
PHPGraphLib
http://www.ebrueggeman.com/phpgraphlib