If you are looking for different ways to carry out plenaries, look no further than this TES page. The powerpoint contains over 130 ideas for plenaries suitable for many different contexts. This really is a good one. You'll need to register (free) to download it. It is quite a large file but worth the wait.
http://www.tes.co.uk/article.aspx?storycode=6017890&firstLoginPage=Y