Sometimes I wish I knew exactly how agents think when it comes to what they'd like to see in query letters, submissions, and what (exactly) it is that they're looking for. Sure some of that information is available on websites & publications like: Writers Market (http://www.writersmarket.com/), and WritersNet (http://www.writers.net/agents.html) among others.
So, I've been on the hunt for great literary agent blogs. And I've found it has been extremely helpful to get insight into all of the things I listed above, and more.
Take this blog entry for instance by Rachelle Gardner from WordServe Literary which gives examples of feedback she's sent to authors with rejection letters: http://cba-ramblings.blogspot.com/2009/04/giving-reasons-for-rejections.html
Here are a few more agent blogs that I've found helpful, check them out. If you have any you'd like to share, please do.
Colleen Lindsay, The Swivet, FinePrint Literary Management: http://theswivet.blogspot.com/
Nathan Bransford, Curtis Brown Ltd: http://nathanbransford.blogspot.com/
The Rejecter: http://rejecter.blogspot.com/
Lori Perkins' Agent in the Middle: agentinthemiddle.blogspot.com
Buried in the Slush Pile: cbaybooks.blogspot.com
Janet Reid's Literary Blog: jetreidliterary.blogspot.com
Jennifer Jackson's Et in Arcaedia, Ego Blog: arcaedia.livejournal.com