The lower photo is on 1 mm grid paper, indicating that the opisthosoma alone is around 5 mm in length, while the total span is just over 15 mm!
This animal is very active, constantly tapping and probing with the first pair of legs and running around. I have no idea what it eats - does it actively hunt invertebrate prey or does it quietly eat bits of the tree it lives on?
I'll have another go at getting an ID of this species; I'll update this post if anyone can shed any light on it.
Edit 14-07-06: Well folks, that was quick and easy, I've got an ID thanks to Bruce Halliday at CSIRO:
Your mite is indeed spectacular. It is a member of the family Erythraeidae (Prostigmata). I think it might be Rainbowia imperator (Hirst 1928) or a related species. These are beneficial predators in the garden, eating aphids and other small insects. The larval stage of the mite is a red parasite that attacks insects and spiders. Other related genera are Erythrites, Paratrombium, Caenotrombium.Thanks Bruce!