The four cores from the original Portal game, made as a follow-up to these guys [link]
Still to be made: Edgeless safety cubes, P-Body, Atlas, GLaDOS, and an ASHPD. Can you tell I like Portal?
I now have the cores listed up on etsy, available individually or at a discounted rate for groups of four or eight. [link]
If you lack an etsy or want me to make something a little different, always feel free to note me here on dA.