Below are some libraries which might help you:
1) http://code.google.com/p/core-plot/
2) http://code.google.com/p/s7graphview/
3) https://github.com/duivesteyn-net/deSimpleChart
4) http://www.rgraph.net/ (Will work on UIWebView only)
5) http://sebkade.wordpress.com/2010/05/06/basic-graph-class-for-iphone/ (a blog where demo is given to create a graph)
