Packing Puzzles

Here, one starts with a number of odd shaped pieces with the objective of packing them back into a cube.

Create a Cube
It's sort of like a Pandora's box, once they come out, it's almost impossible to get them back in.
Impuzzables
If you really can't get enough of packing puzzles.  Lakeside Games produced a series of these of varing colors and levels of difficulty.