http://waynesword.palomar.edu/plsept99.htm
Good reading on "weight" of woods.
LBR - take a look.
Some of the heaviest hardwood trees and shrubs of the United States have specific gravities between 0.80 and 0.95; including shagbark hickory (Carya ovata), persimmon (Diospyros virginiana) and ironwood (Ostrya virginiana) of the eastern states, and canyon live oak (Quercus chrysolepis), Engelmann oak (Q. engelmannii), hollyleaf cherry (Prunus ilicifolia) and Santa Cruz Island ironwood (Lyonothamnus floribundus ssp. asplenifolius) of southern California.
Not that they'd make great riser woods, just that they are very dense.
Pick gorgeous woods that you love for your bows. Have the bowyer add extra micarta to the riser - aint that the best way to add weight to the riser Chad ??