I get the newsletter from the Nelson Literary Agency and frequently read her blog. It’s always got good info and I recommend it to all writers who intend to publish someday.
Her February newsletter there was an article from her assistant, Sara, that talked about issues surrounding e-mailing queries. (Scroll down to the cream part.) I thought it was very good and I’ve had the same issues.
Other recent posts on Kristen’s blog that I think you should check out: