A no-prep game my students really enjoyed was "Secret Cinderella," a modified version of the turn-left-turn-right variety of the game. 2 students were competing "princes" and left the room. While they were gone, I picked one volunteer to be a the secret Cinderella (they had to know that by being Cinderella they might have their looks picked on by their classmates). I had other students raise their hands and contribute sentences to describe that student, e.g., She has long hair, and I typed them onto a PPT screen. (You could also write them on the board.) I limited it to 3-4 sentences to keep things moving and not make the description too specific. I didn't allow negative comments like, "He is ugly." Then the princes would come in to a fanfare and have to read the screen and ask students, "Are you Cinderella?" to which they had to reply "yes" or "no." My co-teacher went out in the hall while I was writing the sentences, to prep them to do this (i.e. to read the clues first and not just randomly approach students) and my co-teacher also told the students not to look at the Cinderella or laugh loudly when the prince got near, because it gave it away and was no fun. I allowed both boys and girls to be princes or Cinderella. But I usually had the 2 princes be either both boys or both girls so they wouldn't get too awkward out in the hall alone together.
Oh, and the first prince to find Cinderella was the winner. We usually played around 4 rounds per class. And everyone was just dying to participate--no one crying from someone saying they had small eyes or whatever.
This worked well after using one of the ppts posted on here as a review--the one with Shrek. I liked it because of the grammatical focus. on is/has, and adding "a" when needed.