Voronoi Region Interpolation
Mathematica 6 can interpolate irregularly arranged data, making flat Voronoi regions when the interpolation order is zero.
In[1]:=  |  ListPlot3D[RandomReal[{0, 10}, {50, 3}], InterpolationOrder -> 0,
Filling -> Bottom, Mesh -> None, ColorFunction -> "SouthwestColors"] |
Out[1]=  |  |