[@Neo Is Delight], suffice to say that at the end of LoK there were about 30-40 airbenders in the temples with hundreds of Air Acolytes, so I'm about ninety percent sure that there are airbenders who can't trace their ancestry back to Aang, even if it is only by a generation before their family are nonbenders.

[Hider=Season 3 Spoilers]Bo Lin and Opal's kids have a fairly good chance of being airbenders. (Along with firebenders or earthbenders) There's one family at least with no Avatar Aang Ancestry.[/hider]