And this from Listener Ian as well:

“You mentioned last episode about wanting to know how the more specialized forms of bending (metal & lightning) came about.  That got me thinking that it seems each of the four major bending forms has a more unique and specialized version (earth – metal, fire – lightning, water – blood) but nothing for air!  This could be because the airbenders were all but wiped out.  Just wondering what your thoughts on this would be – what could the specialization of air be and will this be explored in the show?”

Hmmmm.

Personally, I think that the Flying Air Sphere is the highest form of Air Bending. We only see Aang capable of flying without gliding while in the Air Sphere in The Avatar State.

But, I should mention that smarter group-minds than this one have put this up for debate and added it to the Avatar Wikia:

“Airbending is the only art that apparently has no specific sub-skill or specialized form that has as of yet been revealed, although it has been speculated soundbending could fit into this category.”

Sound Bending is when Aang uses his air to amplify a sound like a Bison whistle, a distracting sound or a call for help.

-Da7e-