'Breathy' sounds
 

I'm trying to get some 'breath' into a sound, so far I've made some decent ones using saturation and reverb on 'flute' style sounds, but not quite what I'm after (which is essentially the intro to Rhubarb, Aphex Twin, S.A.W.II). Any tricks or techniques?

I don't know if this is what you are after, but last night I stumbled upon some sounds that seemed rather "breathy" to me. I turned FM Amount up a bit, to around 18 or so, and then I set the FM Mode to noise. Maybe that might do the trick for you.

That's a good trick, and one I use too (think Ferry Corsten - Sublime).

The obvious one is also adding standard noise. Use the filter EG to morph it over time.