There were several ideas that I came across at the Rick Morris seminar a couple days ago in Santa Rosa. A couple days ago, I mentioned the differentiation of hand signals. He also mentioned the use of music to initiate transitions. So, for example, he suggested using the Mission Impossible theme song to mean that school is about to start, so everyone needs to have their homework out, get off the computers, get in their seats, and be facing the board before the song is finished. The theme song is about a minute, so that's perfect.
There are a couple things that should be considered when using musical transitions. #1 You need to train your students in how they will respond to each particular musical transition (if you have more than one). I guess if you wanted to have a little fun with it, you could paint the picture as though they're on a mission and they need to complete their mission before the time runs out (i.e. get everything ready before the song is over). I think most kids would get a kick out of that.
#2 What do you do if a student doesn't properly respond to the song? This is my best guess. When you have time, such as during recess, take them aside, and ask the student what the song means. If they've heard it enough, they should know what it means. And then, take time out of their recess for not responding to the song as everyone else is.
Anyway, the musical transitions idea is pretty cool. I think I'll utilize it once I have my own class.