If you haven't already seen, I wrote a charting widget for Gtk/Cairo. Over the last fews days I have been adding annotations into the package. Annotations allow you to add arbitrary lines, circles, stars, images, text, etc to a chart. Annotations can be used to add non-data information to a chart like trend lines, and resistance and support, or, you can add purely visual elements like images to enhance the readability of the chart.
