Even if you aren’t looking representation, she’s an excellent source on the agenting/publishing industry. Besides tips on writing a query or a book proposal, she has a list of other agents who blog and websites for writers. Kind of makes what I do here look pitiful : ).
Finally, she has an archive of some of her most insightful posts. Definitely check these out. There’s one on what to do if an agent calls (ah, the dream!), another on what questions to ask…I advise adding the site to your blogroll right now because she’s always posting something useful.
I know not everyone wants or needs an agent. That's fine. But it's still helpful to read about the industry from an insider's perspective, and you can't do any better than Rachelle Gardner. Needless to say, she's also on Twitter.