Google has released an open web API, which provides drop-dead graphs and charts for web pages. I really find their implementation elegant and powerful. Here are some sample charts and their usage urls. Good stuff!
Linear stripes Chart
Actual url: http://chart.apis.google.com/chart?cht=lc&chd=s:UVVUVVUUUVVUSSVVVXXYadfhjlllllllmmliigdbbZZXVVUUUTU&chco=0000FF&chls=2.0,1.0,0.0&chxt=x,y&chxl=0:|Jan|Feb|Mar|Jun|Jul|Aug|1:|0|25|50|75|100&chs=200×125&chg=100.0,25.0&chf=c,ls,0,CCCCCC,0.2,ffffff,0.2
Linear gradient Chart
Actual url: http://chart.apis.google.com/chart?cht=lc&chd=s:pqokeYONOMEBAKPOQVTXZdecaZcglprqxuux393ztpoonkeggjp&chco=FF0000&chls=4.0,3.0,0.0&chs=200×125&chxt=x,y&chxl=0:|1|2|3|4|5|1:|0|50|100&chf=c,lg,0,76A4FB,1,ffffff,0|bg,s,EFEFEF
Here is the blog post announcing the public release of the Google Chart API
And, here is the Google Chart API reference page