pins in the feet, and a pin vise or exacto handle to hold it. base work is done separately, with the model placed prior to the pin (but after the hole) so i can drill the matching hole in the base before painting. also have a few hemostats (curved and straight) floating around from my days are a body piercer, and they get pressed into service from time to time as well. I've also got a nice fat wine cork, and a tapered cork attached to a 40mm base for holidn models.
When I was painting my Otergas, I had 3 pin vises (they've just shown up or been left with me over the years), an extaco handle, and a pair of hemostats holding the models since I was going to be doing their denim at the same time to keep the colors consistent. Witch Hunters saw 3 pin vises, an exacto, and a cork.