Naruto - part 1
Dragon Ball - Oolong's wish, Krillin's death, Goku's 2nd death, Krillin's 2nd death, Upa's fathers death (probably the sadest moment in all Dragon Ball xD) and of course the ending of DBGT. Pretty much every arc had a sad moment.
One Piece - Arlong Park arc, Baratie arc, Zoro's past, Luffy's past, Drum Island arc, Water 7 and Ennies Lobby effin cryed like a baby when Ussop left and little Robin met her mother.
I always try to resist like a man but Water 7 and Ennies Lobby had me crying river of tears. Dragon Ball GT had a tearful ending.