I'm working on a query letter now. They seem to be as much of an art form as novel writing, with no of the fun of being able to make up details. ;)
I'll post what I come up with when I finish.
Sources that I used to figure out what to do and what not to do include:
How to write the pitch paragraph: http://pubrants.blogspot.com/2007/10/pitching-and-all-that-jazz.html
What to do:
http://pubrants.blogspot.com (The various sample queries.)
Query Shark: http://queryshark.blogspot.com/