http://drupal.org/project/quant seems to present some powerful graphs, that reads of the database. I have been reading and most of the information seems to point to data on a static table - not too useful in my opinion. In that case, do it in excel, get an image and upload it and you will be done with the torture that Drupal chart creation seems to be (for beginners at least).
Now, taking the graphs produced within the Drupal Commons environment, which produce a timeline of data + other pie chart type data, that reads off ones data base seem impresive to me. The question, where can we learn or read about how to point to the data "we" want to graph.
I will not dive into my particular need, but with the interest of keeping the discussion open, and informative by hopefully attracting someone that can guide me, and probably others that might interested in powerful solution.
Here is a link, that shows some of the graphs generated by the system: http://screencast.com/t/YjFjN2My