Previously, I've blogged about the importance of experiencing joy in the classroom: more-classroom-community-building-activities.html. Just to reiterate, this is so important because during the year your students are going to have to trust you. As teachers we are going to have to ask them to do some difficult things and to put themselves out there (I know that is true for me in my reading intervention program). If you've also had fun together it makes it easier to do some challenging work together.
Volleyball- This is one of my favorite activities yet. We took 20 minutes on a Friday (minimum day to boot). I hung a piece of yarn to divide the classroom, got the chairs out, and a ballon out (see picture for set up). Then we played volleyball. While some teachers might use those Friday minimum days to show a movie, I'm a huge advocate of using time like that to build connections.