I have to 'fess up - Toby's sacrifice for Tanya does it for me. You can't deny, it's a powerful moment.
Wolfgang's sacrifice for Gabriel, and Gabe's recovery of the Schattenjager amulet, is similar - except it's more of a "What the hell...? Oh, this is so f***ed up" moment, the kind where you don't know if to choke up or to grind your teeth in fury.
OTOH - call me an old sentimentalist if you like, but Malia's sacrifice for Gabriel is definitely one of those weepy moments.
It's funny - most of these moments happen when some character sacrifices him/herself for another, but the big sacrifice scene at the end of QfG5 never affected me in that way. *shrug* I don't know why, it's a strange thing.
Name your 'favourite' weepy-moments!