This is my theory on why its called the leaf village:
Well, a tree has many branches on it right? And each branch produces a whole bunch of leaves. Well, in the leaf village, the branches really represent all the ninja's (including villagers) and each ninja is specialized in his/her own technique(s) (like Shikamaru's family only use their Shadow's while Kiba's family work together with their dogs). I guess thats another reason why the leaf village is called what it is. But I guess the First Hokage's tree jutsu works also.

EDIT: I forgot to add that the leaves would be all of the ninja's techniques (like Naruto's branch would have Kage Bunshin no Jutsu, Sexy no Jutsu, Harem no Jutsu, Summoning, etc.)