gdchart is a fast graphing extension written entirely in C. It can handle most common types of graphs with the only major missing feature being that it currently doesn't handle legends. Either create your own legend beside your graph, or maybe even layer it into the background image of your gdchart graph if you have a static legend.

Line Chart
<?php
 Header("Content-type: image/png");
 $chart = new gdchart(LINE);
 $chart->add(array(2.5, 5.1, 8.6, 12.0, 15, 9, 8, 7));
 $chart->add(array(5.0, 8.0, 9.2, 10.2, 7, 8, 10, 9));
 $chart->add(array(8.0, 10.0, 14.0, 18.2, 16, 14, 12, 10));
 $chart->labels = array("Jan","Feb","Mar","Apr","May","Jun","Jul", "Aug");
 $chart->colors = array(0x1133aa, 0xaa3311, 0x33aa11);
 $chart->out(640,480,IMG_PNG);
?>
Output
Line Chart with custom axes
<?php
 Header("Content-type: image/png");
 $chart = new gdchart(LINE);
 $chart->add(array(2.5, 5.1, 8.6, 12.0, 15, 9, 8, 7));
 $chart->add(array(5.0, 8.0, 9.2, 10.2, 7, 8, 10, 9));
 $chart->add(array(8.0, 10.0, 14.0, 18.2, 16, 14, 12, 10));
 $chart->labels = array("Jan","Feb","Mar","Apr","May","Jun","Jul", "Aug");
 $chart->requested_ymin = 0;
 $chart->ylabel_density = 25;
 $chart->ylabel_fmt = "%.0f";
 $chart->colors = array(0x001133aa, 0x00aa3311, 0x33aa11);
 $chart->out(640,480,IMG_PNG);
?>
Output
3D Area Chart
<?php
 Header("Content-type: image/png");
 $chart = new gdchart(AREA_3D);
 $chart->depth = 5;
 $chart->xtitle = "Fruits";
 $chart->xtitle_color = 0xffff00;
 $chart->bg_color = 0x112233;
 $chart->xlabel_color = 0xffffff;
 $chart->ylabel_color = 0xffffff;
 $chart->colors = array(0x30ffff00, 0x30ff00ff, 0x3000ffff);
 $chart->add(array(2.5, 5.1, 8.6, 12.0));
 $chart->add(array(5.0, 8.0, 9.2, 10.2));
 $chart->add(array(8.0, 10.0, 14.0, 18.2));
 $chart->labels = array("Apples","Oranges","Melons","Pears");
 $chart->out(640,480,IMG_PNG);
?>
Output
Pie Chart
<?php
 Header("Content-type: image/png");
 $chart = new gdchart(PIE_3D);
 $chart->title = "This is a Sample Pie Chart";

 $chart->title_font = "/usr/share/fonts/truetype/CANDY.ttf ";
 $chart->title_ptsize = 24;

 $chart->label_font = "/usr/share/fonts/truetype/Jester.ttf";
 $chart->label_ptsize = 16;

 $chart->edge_color = 0x000000;
 $chart->labels = array("red","green\r\n(exploded)",
                        "lt blue","purple","missing","cyan","blue");
 $chart->add(array(12.5, 20.1, 2.0, 22.0, 5.0, 18.0, 13.0));
 $chart->missing = array(FALSE, FALSE, FALSE, FALSE, TRUE, FALSE, FALSE);
 $chart->explode = array(0,40,0,0,0,0,0);

 $chart->pie_depth = 30;
 $chart->perspective = 0;
 $chart->pie_angle = 90;
 $chart->label_line = false;
 $chart->percent_labels = LABEL_ABOVE;

 $chart->out(640,480,IMG_PNG);
?>
Output
Combo High-Low-Close Chart
<?php
 Header("Content-type: image/png");
 $chart = new gdchart(COMBO_HLC_AREA_3D);
 $chart->title = "High-Low-Close On top of an Area(volume) Graph";
 $chart->depth = 5.0;
 $chart->angle = 50;
 $chart->annotation_font_size = FONT_TINY;
 $chart->anno_note = "Earnings\nReport";
 $chart->anno_point = 8;
 $chart->vol_color = 0x40806040;
 $chart->grid = TICK_LABELS;
 $chart->ylabel_density = 40;
 $chart->hlc_style = HLC_CONNECTING | HLC_I_CAP | HLC_DIAMOND;
 $chart->add_scatter(17.0, 3, SCATTER_TRIANGLE_UP, 0x50808060, 30);
 $chart->add(array(17.8,17.1,17.3,17.2,17.1,17.3,17.3,17.3,17.1,17.5,17.4));
 $chart->add(array(16.4,16.0,15.7,15.25,16.0,16.1,16.8,16.5,16.8,16.2,16.0));
 $chart->add(array(17.0,16.8,16.9,15.9,16.8,17.2,16.8,17.0,16.9,16.4,16.1));
 $chart->add_combo(
   array(150.0,100.0,340.0,999.0,390.0,420.0,150.0,100.0,340.0,1590.0,700.0));
 $chart->labels = array("May","Jun","Jul","Aug","Sep","Oct","Nov","Dec","Jan","Feb","Mar","Apr");
 $chart->out(640,480,IMG_PNG);
?>
Output