A while back, I did a walk-through on how to make a hexagon grid in 3DS Max and tonight I did the same thing in Houdini with SOPS. I was going to put together another tutorial about it but it's the exact same math as I outlined in this post so I'll spare myself the time. The Houdini setup has more controls and is easier to use though.
Check out some screenshots
The density parameter allows re-scaling of the grid
The height can be randomized with control of the upper and lower limits as well as control based on proximity to a point, in this case the center of the sphere
The limits can be reversed
The density parameter is technically limitless but since it's copied SOP geometry, it's going to require some RAM. I went up to 160,000 hexagons without any trouble but it bumped my ram usage up to 1gb