Rare LEGO parts are always interesting.
I own some old rare multicolored LEGO bricks from the early 1950s:
http://www.brickshelf.com/cgi-bin/gallery.cgi?i=5558741
I have been told, that this bricks were made, when there were changed colors in the molds, and they were sold cheap to the LEGO employees. Today they are very rare to find and very expensive.