This interactive resource is useful for demonstrating the volume of cubes and cuboids.

Instructions
http://www.teacherled.com/2008/09/09/cuboid-exploder/

Resource
http://www.teacherled.com/resources/cuboidexplode/cuboidexplodeload.html

Bill Newell has kindly shared some Google Sketch-up files on volume and cross-sections that he has created.

Google Sketch-up is a free 3-D drafting and geometry tool that can be downloaded from:
http://sketchup.google.com/

The files have been zipped, so you will need to unzip them before you can your them.