pin
or lever
or button
There's several out there

Antares uses a lever
Keleven uses a pin
Micron2 uses a button (but pin shows to left of mouse over)
I think MotoXP B1 uses a tiny button (but it doesn't always work)

some also throw in a transparency button (AlienTechnology's for me works the best - different setting each time you click it)

some throw in a minimize to tray button.

It's usually the pre-perpixel skins, I think it has to do with midi button and transparency doesn't mix