It would be helpful to be able to click on a list of snap points like mid-point of line, center of circle, etc that you can snap to, or use a key to force a particular snap. Perhaps with a change in cursor to reflect the point being snapped to, e.g. a circular cursor when snapping to the center of a circle.
(I know this is right out of AutoCAD, but that doesn't by itself make it unworthy.)
