I've seen lots of raytracers with spheres in it, planes, nurbs,
blobs, and so on, but never one with cubes.

That's why I made one with cubes.

You can download it here:

http://www.perilith.com/~lode/trixel/Files/Trixel002.zip

Use arrows + mouse to move, b to place a block in front of you, and
F1 --> F6 to open different levels. Additional commands are in the
included readme file.

Please give comments.

Thanks.