I've been working on my query letter on and off for quite a few months. It's pretty tight now after lots of feedback and I'm reasonable happy with it. Having said that though I never over look a bit of query advice. Who knows what sort of gems one might glean!
I discovered this post by the author Shawn Klomparens over at Writer Unboxed today. He offers some awesome advice on writing kick ass query letters and breaks down one of his own to show us the process and over advice at each point.
Honestly, if you are querying for going to be in the near future, check this out!
I'll definitely be checking my own against this advice.