Arrowhawks: does anyone remember ever using or encountering them? I don't blame you: there's much better Plane of Air encounters than a lightning-shooting four-winged bird.
What can an Arrowhawk do? It is able to fire lightning once per round (about equal to Acidic Splatter), is immune to lightning, acid, and poison resistant to fire and cold, has natural armor, various ability score bonuses, perfect flight speed, a natural bite attack, and the excellent outsider type that makes its 3 RHD much better.
Of course, a strong base creature isn't enough: it needs to remain relevant at higher levels. Fortunately, the arrowhawk is able to do so. A roguish build will appreciate the high skill points and ability bonuses, not to mention the fly speed, and I can definitely see one stacking up to a 4th-level rogue. Final LA: +1.
There's also the adult (7 HD) and elder (15 HD) arrowhawks, but they're so incredibly similar that I'm not going to evaluate them thoroughly. -0 LA is the only fair option.