While working on a project I found out that HighCharts is the best to display graphs on webpage as it has less overhead and requires less space. But the biggest challenge was to implement it using php and not jQuery. We will implement it using MVC pattern as CodeIgniter follows the same.
Included in the post is a library for interacting with HighCharts from PHP, configuration settings for CodeIgniter and the model/view/controller pieces to tie it all together. You can see an example of the end result here.