Any compass that will hold a regular pencil usually holds an Exacto handle. You can get them from under a buck up. Exacto makes one as well. Try to find a bow compass so that it does not move while cutting. You can make a bow.. sorta... by putting two pieces of metal accross the compass and using a small bolt and wing nut, so that the adjustment does not slip when cutting. I have a larger one that is actually three parts that use a yard stick. One piece has the point. One uses drafting lead and the third holds an Exacto Knife. I use it to cut larger arcs. I got that one a Michael's Crafts years ago.

For more irregular shapes you can make a template from plastic. The stuff like you would use on an overhead projector. Then, use it to carefully cut along the edge. While your looking in the stationary store, pick up some overhead projection markers. They are water soluable and work well to draw on the film. Then, just wipe it off with a wet Kneenex. Heat has no affect on them either.

JR