Today we printed designbynumbers' Center of mass manipulatives for calculus classes from Thingiverse. It worked very well and balanced wonderfully!
Thingiverse link: http://www.thingiverse.com/make:90962
Settings: Printed on a MakerBot Replicator 2 with .2mm layer height. We changed the infill to "linear" instead of "hexagonal" because the hexagon-filled one seemed not to balance quite right. With linear infill the balance was spot-on.