I've linked to Teresa Nielsen Hayden's blog several times. It is one of the best blogs on the net, has one of the best communities of commenters I know, and is generally a great boon to all mankind.
One of the blog's best features is TNH's occasional posts about writing, editing and publishing. Being a writer, as well as an editor at a major publisher (Tor), she knows whereof she speaks.
When people asked Neil Gaiman about literary agents, he did a pretty smart thing: He asked TNH. She answered, and Gaiman posted it in his blog in a post he called Everything you wanted to know about literary agents… And rightly so. Anyone interested in writing professionally should read it.