This suggestion is similar to the "Color by size" suggestion below.

"This feature would help those that are using your Rasterbator to create templates for other projects ( like this: http://imgur.com/gallery/qEpis ) ...so that it is easy to judge how big or small a circle is without having to measure it."

No measuring would be needed in this case as the circle sizes would be listed.

Using a text based file would eliminate the need for a finite number of sizes that would be needed in order to match each size to a different color in the above suggestion.

I assume this information is already being generated to create the Rastorbation anyway. I'm simply suggesting the end user be able to access it directly.