A very interesting way to reduce iso noise is to take several images. Due to chaotic nature of the noise, and static nature of the reality which is being photographed, one can achieve less noise result at high sensitivity.
You simply need to merge achieved photos with average transparency values.
M = merged. At iso 50 it's barely useful, but at iso 400 it's good enough. (Sorry for such crappy photo, it's old and i don't want to remake it.)