Anthropomorphic bats: now with more lore.
Nycters are small monstrous humanoids with 3 RHD, a weak 1d4 bite, a reasonable fly speed, racial bonuses to dexterity and wisdom (combined with penalties to strength and charisma) and the rather interesting Hunting Cry, an essentially-friendly 30 ft. cone of sonic damage and multiple-round paralysis that can be used every 2d4 rounds.
Obviously, paralysis is a rather useful save-or-lose that can win encounters (especially when it's this big a cone). The creatures that are immune to it are hard to overcome, but a lot of those lose to flight (especially at lower levels when being a nycter is contributing relatively more to the total PC).
In the end, the nycter's rather useful ability, flight, and not-awful chassis are worthy of +0 LA.