Two more tips on querying from Miss Snark's archives:
From 3/9/07: "There are people in your office right now with a run in their stocking, unshined shoes, three weeks past due on a haircut and drenched in Eau de Gauloise, but that is NOT how they showed up for the interview that got them the job. A query letter is like a job interview: put your best foot forward. And remember, the default answer on query letter is NO. What I look for is something that makes me say YES."
From 3/18/07: "Nothing beats plain straightforward description in a query letter. It's when you get all fancy that you shoot yourself in the foot. If your description sounds like a snotty wine waiter at an overpriced faux french bistro "a clever little novel drenched in atmosphere with an insoucient streak of historical je n'est ce quoi circa 1832" then you've just assured me that not only is the novel not quite right for me, it will need a trip to Lourdes to be publishable."