Thimblebug posted the thread I was going to suggest. It's a fabulous resource and a wealth of information. Lots of very talented quilters on that thread. Read through those pages and you're sure to get loads of ideas.
I would also add: make sure your group decides beforehand on the size increment for each round, i.e., 6 inch, 9 inch, etc. Otherwise, you might be faced with a very strange sized round. ((worst case scenario - add a border to make it a more manageable measurement)).
Also, Google Round Robin or Medallion quilts and you'll get tons of ideas!
Have fun and please share pictures!
Jane