The language of the Romans, and from which RomanceLanguages are descended. The EnglishLanguage still retains many Latin phrases; some of these are:
Also, Latin is the New Perl: see PerliGata
For most "Latin phrases" bandied about for humorous intent: see DogLatin
My personal favorite: morituri te salutant
What about ArgumentumAdHitlerum? Curiously, I've been compared to Hitler by my detractors on a number of occassions. Anyway, my favorite is the lyric for Monteverdi's Domine Ad Adiuvandum, 1610 Vespers:
Deus, in adiutorium meum intende: Domine, ad adiuvandum me festina...
...and don't tell me you don't love benedicamus domino like in German Christmas carols.