Earlier this week I released the FusionCharts drupal module.
http://drupal.org/project/fusioncharts

There are a number of charting modules available for Drupal these days, but in my opinion, this is the best. It has an API that allows charts to be drawn from a SQL query, or from an array of data, or for graphs to be created using a user interface, or from the views module.

This module connects Drupal with the FusionCharts Free package. FusionCharts Free is a flash charting and graphing component that can be used to render data-driven & animated charts for your web applications and presentations.

What's included in this module:

* A content type with an graphical user interface for creating charts
* An API that to create charts using SQL queries
* An API that to create charts using an array of data
* An API that allows for drill-down viewing of data (you can click on the bars to fetch new data)
* Basic views integration
* Basic documentation

Graphs and charts supported:

Single Series Charts:
* Column 3D
* Column 2D
* Line 2D
* Area 2D
* Bar 2D
* Pie 2D
* Pie 3D
* Doughnut 2D

Multi-series Charts:
* Multi-series Column 2D
* Multi-series Column 3D
* Multi-series Line 2D
* Multi-series Bar 2D
* Multi-series Area 2D

Stacked Charts:
* Stacked Column 3D
* Stacked Column 2D
* Stacked Bar 2D
* Stacked Area 2D

Combination Charts:
* Multi-series Column 2D + Line - Dual Y Axis
* Multi-series Column 3D + Line - Dual Y Axis

Other Charts:
* Funnel Charts