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:
New Rules for Promotion (about websites) which links to this post, also about websites
YA Top 25 (things they see too often in YA submissions)
Daily Digest Reading (a list of recommended reading for those who are serious about publishing in a national market)