I stumbled across this great site full of activities for developing group dynamics through experiential activities. There are loads of free downloadable pdf docs on activities that are fun, require very little in the way of materials, and are pretty simple to carry out (well, as simple as any group activity is!) and can be aimed at various levels of reflection or self discovery.
I especially found the section on Exploring the Five Stages of Group Formation helpful, and recommend this for anyone who is working with a group of people over several weeks. I think so many group programmes are simply 1:1 sessions carried out with a lot of people rather than truly becoming the synergist venues for developing as people and achieving goals that they really can be.