Valve sold out of Weighted Companion Cubes in about twenty minutes. Or so it would seem; I didn't even see the Steam notification that they'd been added to the store before they were gone. Rumor has it they fetch a pretty penny on eBay too.
For Christmas,
my girlfriend sewed me my own Weighted Companion Cube. She's a whiz at such things, as evidenced by the below photograph.
I think it looks about 1000x better than the ones Valve had for sale anyway.