My mate has just been up to my house with a new toy
It's called TrackIR by NaturalPoint
and it's an awsome bit of kit that integrates with FSX.
You put a sensor on your head and an IR tracker on top of your screen and as you move your head it controls your view on the screen. It works flawlessly in all axis.
I've taken some video footage with my phone and i'll put it on YouTube some time soon and post a link.
EDIT: just found this
on YouTube. Explains it very well.