Some possible features:
--rotating (already available)
--inverting/desaturating/other color alterations
What it might be like:
Perhaps the image editor would keep a temporary history to allow several undos. This could probably be limited to 3 or 5 states, to save space. It should probably keep the image currently being edited in a temporary location, and it would give you the option to save the image normally or save it as a new image.
Does anyone like this idea?