Here are some awesome web charting libraries to make it easy to create nice-looking graphs and charts for your website:

• Google Charts - Free. Polished.
• JQPlot - jQuery plotting library
• Flot - jQuery plotting library
• Highcharts JS - A JavaScript charting library that looks polished. Free for non-commercial use, pay for commercial use.
• RaphaelJS - vector graphics library
• gRaphael - uses RaphaelJS to create “stunning charts on your website”
• Bubble Charts - bubble charts only
• D3 - data driven documents. nice animations.

And some articles about charting

• Top 5 jQuery charting libraries
• Flot vs Google Charts on Stack Overflow here and here
• Hans Rosling’s awesome visualization video of 200 Countries, 200 Years, 4 Minutes