here are a couple of 30.9s...
....that I have looked at
no set-back (ie straight)
-thomson (350/400mm)
-easton zero carbon (400mm)
set back (ie with offset)
-richey wcs non-carbon (350), pro non-carbon (400) & comp (350)
-thomson (350/400)
-easton MTB (350), EA50 & 70carbon (350), EA70(400)
-Race Face Next, XY, Atlas, Diabolous, evolve (all 350)
An option is running a normal post, say 27.2 with a shim up to 30.9 (USE makes a good one here in Europe) - this is a clean (and light) solution, but a pain if you are moving your post up and down a lot. I guess if you want a full combo (bar, stem, post, headset, crank) you can't go past Race Face. But I have to say my fave is still Thomson because the black anodising is of a very high quality and doesn't rub off when you move your post up and down a lot....and it combines great with the new X4 stem!
Grüsse Anthony