This may not be Kosher with the Lego purists out there, but I milled up a Lego brick with studs on both surfaces. Basically, it has two male ends instead of the traditional one male, one female.
Side note, I used old floorboards as the stock material (maple I think). This may be the perfect material for small desktop CNCs. Flat, milled hard wood that is essentially free. Just watch out for nails.
They are re-doing the hardwood floors at ITP. And I was lucky enough to reclaim (grab) some old boards. Was pulling nails from them for a couple of hours yesterday. Tons of scratches, nicks, and character.
Soon this material will be turned into furniture or lamps or something.