Interesting volume datasets I've collected:

------ Public Domain Datasets (prepared by Orion Lawlor) ------

Worldlight: 128x128x128 global-illumination volume dataset, "tree" universe, voxel_gi sweep method.

grid_*: cubic grids of various sizes.  Generated from a 1.3m particle astrophysics dataset from U. Washington researcher Tom Quinn.

mset: 100x100x100 3D mandelbrot set generalization.  I think this one's of my own bizarre design, *not* the standard quaternian 4D mset.

------ Not Public Domain ----

head128: 128x128x113 MRI dataset of a human head, from 1998 SDSC splatter distribution.  The same dataset as in my "SliceViewer" program.  Generated with "convert -depth 8 -size 128x14464 gray:head128.dat head128.jpg".

vishu128: 128x128x128 cryosectioned human head, from the NIH Visible Human Project.  Slices reconstructed from the MPEG cross sections at http://www.sci.port.ac.uk/rad/mri.htm.

vishu256: 256x256x255 cryosectioned human head.