I'm not sure about the most tearjerking moment for me, but the ending of Doctor Horrible's Sing-Along Blog has me misty-eyed by the end... Damn you Neil Patrick Harris...!
Vixxy said:End of Xenosaga III... (Huge spoilers)
Jin's death
I loved his character and his death, although really bad ass, always makes me cry. Such a great way for him to go out.