interesting. I'd call it a spike too (and yea, its in nearly every office around here. I always see it in diners and restaurants too, diners especially, right next to the cash register).
so on ebay if you look up 'check spindle' you get the normal cheap ones for $2. If you look up 'paper spike' you get old "vintage" ones from the 50's, lol, selling for like $30. (I like your tastes, ricercar
Not many hits for any of the other terms. even memo spike only had one hit. Of course I was originally searching for 'stake' and 'needle' and 'paper pinner downer' - no hits at all.