One that I have heard differently from campus to campus is Pi Kappa Alpha. On some campuses, they're Pikes, on others, Pikas. They're Pikas at our school.
I've heard that Alpha Delta Pi is known as Alpha Delts, but for the most part, we're ADPi's.
I think that there are nasty names for every GLO, but [high horse] I refuse to use them [/high horse]!