Here is a list of sites that provide armature kits for use in stop-motion animation.
Skeletoon - Ball joint. A French company. I am currently seriously considering buying one of their kits.
Model Armatures - Ball Joint. The joints on these armatures seem a little too chunky for what I would want. They do offer strong magnates for sale as well though.
Arma Benders - Ball Joint. They seem decent enough but expensive considering they don't have hands.
Animation Supplies - Ball Joint. I was originally considering these armatures but the price was putting me off despite how brilliant they appear. I know these things don't come cheap. Now I may use this site to buy puppet hands and some rigging for the skeletoon armature.
STOP-MO-TEC - Aluminium Wire. May be more useful for supporting characters who do not take up much screen time.
Animation Toolkit - Aluminium Wire. Another consideration for supporting characters.