I've been thinking about closing argument as I prepare for a trial that begins next week. For those looking for some tips on organization, here's an article simply titled "Closing Argument." I'm not sure who the author is, so I'm unable to attribute the link. (Note to authors: if you're going to put your stuff on the Internet free for the taking, put your name on your articles.)
Here's another tip: if only until your closing is concluded, you have to genuinely believe in your client and your client's cause. If you don't, the jury will see it in your tone of voice, your body language, etc. -- and they won't give you the result you're hoping for.