Try this one, Grave of the Fireflies (Hotaru no Haka). It will DEFINITELY jerk the tears out of your soul. I have watched this movie once and don't have the plan to ever watch it again. Not because it's a bad movie, believe me, if any, it's one of the best out there, and it's one of Isao Takahata's best creations, and he's one of the founders of Ghibli. It's just that it's toooo sad, I don't think I could bear the sadness one more time. I've watched a lot of tearjerkers, including one litre of tears, a moment to remember, nobody knows, etc, etc, but this one is number 1 on my tearjerker list...
But definitely a MUST watch, even if it's only once in your life...
Ps. Oh, one more thing, watch the original one from studio ghibli. This one here[/URL]. [U]Not the Live Action one.