I'm totally stealing from all the agent blogs I'm reading today, for which I offer the sincerest apologies; they should just think of it as inspiration. Nathan Bransford has a post about Query Letter Formatting.
I'm going to one-up it a tiny bit, and add that not only do I agree with his post, but I also think that it is entirely unnecessary to send *things* with your query letter.
What do I mean by things?
Well, for example, a few years ago there was the infamous query letter that came with green parrot feathers. Yes, actual parrot feathers. We hung them on the office bulletin board for decoration. =)
So, all the authors and editors and slush readers who read this blog... what strange *things* have crawled out of the slush pile for you? Feel free to be anonymous when posting, as understandably, no one wants to identify themselves as the agent that received a giant pair of heart-patterned boxers, right? (just an example; I really haven't gotten that one)