I have a feeling this is going to be answered ridiculously fast, and I'm actually somewhat embarrassed to be asking it, but I seem to be not-quite-capable of figuring it out myself.
The opera song they use from 2:30 to 2:45 of
http://www.youtube.com/watch?v=_W93BsoJDKk . I heavily suspect it's from Carmen. Specifically, the 1984 movie version staring Plácido Domingo, since I'm fairly certain I recognize that voice. It's probably a really famous and obvious song, too--I know it's been sampled a lot, like...well, here, for example. It's just that my Google and YouTube skills are apparently weak and I can't find an actual song title or track listing or anything beyond "it's probably in Carmen somewhere" for anything except
Habanera, which isn't it.
Edit: Wow, I managed to get every single detail of my guess wrong (not Carmen, maybe not Plácido Domingo though apparently he recorded a version too and I'm having remarkable difficulty telling the voices apart,) but still got an almost instantaneous answer anyway.
"Vesti la guibba" from Pagliacci. Thanks,
stephe!