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