As HTML5 catches up steam we can expect more and more awesome graphics. SVG and HTML5 canvas based charts are the most common implementations of the same.
Google charts is awesome in many respects and I have been using them extensively for most of the times. These graphs are such that I give data points and they plat a beautiful graph for me. I wanted the exact opposite thing. I will plot a graph and the user will move the data points and give me the data values which I will then save.
I did not find many libraries meeting this unique need of mine. So i have built one : https://github.com/akshar100/Rapheal-Drag-Chart
This library is going to be of production quality over time.