Here is a new blog by an author* whose agent just sold her debut novel to Bantam. She posts two successful query letters.
And here is what her agent said about her query.
BTW, I read PubRants daily. You can get a lot of good info from this blog. I highly recommend it.
*Caution--If you go to Sherry Thomas' website, be warned that she writes romance and there are some explicit scenes. I stopped reading as soon as I hit those. My endorsement here is of her sample query letters ONLY.