If you are hunting for an agent and haven't discovered agents who blog yet, you don't know what you're missing. Of course there's the obvious things you can learn from them such as what they're looking for, how they'd like you to submit, and that kind of thing. But there is also a wealth of knowledge that many of them are willing to share through their blogs. And then there are those who offer up their services through contests they run on their blogs.
The dynamic Nathan Bransford of Curtis Brown Ltd. runs contests all the time and offers up not only advice on writing, but great information about the publishing industry. Nathan's blog is not something you want to miss. His posts are like tiny jewels of knowledge that he generously shares with his readers. He even has a sidebar titled 'The Essentials (Please Read Before You Query)', how great is that? http://blog.nathanbransford.com/
Kristen Nelson of the Nelson Literary Agency posts the queries her clients wrote that hooked her and explains what she loved about them. She also gives a tutorial of how to pitch. The entire blog is like gold to someone who is on the agent hunt. You don't want to miss it. http://pubrants.blogspot.com/
My own fabulous agent, Ken Atchity, blogs as well. Ken is much more than just an agent though, he is a literary manager. If you aren't sure what the difference is be sure to check out his blog and website. His blog is full of great information about not just the publishing industry, but the entire entertainment industry. http://kenatchity.blogspot.com/
There are a lot of other fantastic agents out there who are kind enough to blog and offer up their advice and experience. When in doubt google an agent you're thinking of submitting to. If you're looking for a list of agent who blog check out the Scribe Sisters blog, http://scribesisters.blogspot.com/. They have an extensive list in a column on the right hand side of their blog. For another blogger with an excellent list of agents check out Lindsey's blog http://thewritewords-lindsey.blogspot.com/