Cover letters
Teresa Nielsen Hayden has an entertaining piece on cover letters, bad and good. Note that the Onion article she links to uses the word "Fucking" in big letters and thus may not be the best thing in the world to read while you're at work, he said, speaking from experience.
The comments people have posted on TNH's entry are also worth reading—click the Comments link at the bottom of the entry.
I refrain from publicly posting examples of bad cover letters that we receive, but at some point I may do some paraphrases (with all identifying information removed, of course) to provide examples in our guidelines of the kinds of things not to do.
Of course, the people most likely to need such guidelines are probably the ones least likely to read them. On the other hand, I think way too little information crosses the barrier between editors/publishers and writers; the more light we can shed on the process, on what does and doesn't work, on what mistakes it's easy to make, the better. It can be very hard to guess at these things from the outside.
Back at Clarion, Chip Delany told us that cover letters had one purpose and one purpose only: to give editors something to file to track stories. I don't think I really believed just how useless they are until I started reading submissions. They do have other purposes, of course: if you have credits that should make the editor pay attention, they allow you to mention those credits. But other than that, honestly, you're better off not providing a cover letter at all than providing most of the information in many of the cover letters we see.