Sarah31, we had a variation of this called "My Tie". The fraternity we were mixing with would bring over one tie for each brother that was planning on attending the mixer (usually the afternoon of the mixer). Then the sisters would choose a tie, go to the mixer, and their "date" for the evening would be the guy who's tie they got. I remember the time my chapter did this, I met a guy who ended up being my date for formal that year!
We also did mix-match (clashing clothes, colors, etc.) and "ER" (everyone dressed up like Dr's and nurses). Okay, I've been out of school for too long b/c that's all I can remember right now! If I think of more, I'll post again.