Sasuke, Haku, Gaara, Neji. They all seem to have had pretty crummy child-hoods that involve the death or lack of family members and it's interesting to see how they all handled it.
Sasuke -> Hunting for the man who killed his family, all we know is that this man has Sharingan and that I THINK he is Sasuke's brother or something...
Haku -> Orphaned and he dealt with it by meeting Zabuza and becoming his "tool".
Gaara -> His family, specificlly his mother was killed and he saw it(this is speculation *shrug*). Like Naruto, a demon was sealed in his body. Unlike Naruto, he believes his purpose to kill everyone except himself.
Neji -> His father died to protect the main family and Byugoken(How do you spell that? :/) power. In his anger, Neji dealt with this by hating Hinata and her side of the Huuyga family and pushed a false belief in Pre-destination. Naruto set him straight though.
In any case, it seems like they all of had crummy childhoods, what I like is the fact that the anime shows the characters dealing with it in different ways, which is very realisitc.
What do you think?