One thing I feel like would be useful would be the ability to draw circles based on the center, rather than the edges. This could speed play up a bit, as a lot of effects are based on where the center is. For example, if you are drawing the area hit by a 40-foot radius spell, you would just need to put the center and the 40 foot radius, rather than mark the center, count out 40 feet in each direction, and then go from there and hope you didn't miscount.
Tangentially related (no pun intended) is on-the-fly shape measuring, where the length/width of a shape you're drawing is shown at the side/top or something, similar to how it's done in Maptools.