Computational results are compared to experimental benchmark results for natural convection of a Newtonian fluid in a cubical cavity. These results are then extended to Powell-Eyring and extended Williamson fluids. Good agreement is seen between the experimental and computational results for most of the Newtonian cases. Results from the non-Newtonian cases are proposed for comparison to future experiments. An issue raised by the Newtonian experimental study is identified and a probable resolution is described. Comparison of Newtonian and non-Newtonian results shows increased heat flux with increasing nonlinearity of the models. The non-Newtonian cases for the diagonally inclined orientation also show periodic behavior not seen in the Newtonian cases.