5 foam core boards
packing tape (for fastening the foam core)
about 2-3 yards white fabric from a sheet or drop cloth, whatever..
1 large poster board. (must be flexible)
1. cut two of the foam cores into a square (save the excess to use as reflectors)
2. tape the foam core into a box.
3. tape the poster board to the back + bottom in a curve.
4. throw the white fabric over the top.
This works best with an off-camera flash so you can experiment placing it in the cube, beside it, top, etc.
Using a digicam is a great way to test lighting.