When I was in the house, we would all turn in a list of guy's names (I think the max was 4) to the social committee, along with what house the guy belonged to, or his phone number if he wasn't in a fraternity. They would compile all the names and send our pledges (in pairs) to the fraternity houses during dinner to read off the names of the guys in that house who were invited. Committee members would call all the guys who weren't in fraternities and invite them. We would always rent a big place and have a band... Crush parties were the best!!
I think my chapter does it slightly differently now, but I'm not sure of the specifics.