I'm not-yet-published, and while I've heard many stories from my published friends, I don't have a whole lot of personal experience. So I decided to gather up some of my favorite sites, written by people who know more than me :)

Querying

Always finish and revise your manuscript to the best of your ability prior to querying agents/publishers!

Query Shark: A no-nonsense guide to writing non-sucky queries.

QueryTracker: This is an awesome resource. Here you can research agents, keep track of your queries and more. There are free and paid options, and quite a few success stories.

Preditors & Editors: Pretty self-explanatory-- before accepting representation, make sure the agent/publisher is legit.

Great Blogs

Nathan Bransford: Nathan has been a very well-respected member of the publishing community for a long time, and even though he's now concentrating on writing and not agenting, he's one of my go-to blogs for up-to-date discussions and information.

Rachelle Gardner: Rachelle is an agent with WordServe Literary Group and always up-beat, friendly, and full of great advice.

Shrinking Violet Promotions: A great resource for introverts worried about jumping into the marketing side of publishing.

Cynsations: Author Cynthia Leitch Smith talks publishing, interviews & promotes authors & in general sends out more information in a day than I can quite absorb! Awesome resource for the children's/YA community!

Professional Guilds

Society of Children's Book Writers & Illustrators: SCBWI is a fabulous community of writers and illustrators and even if you're not-yet-published, you can join and learn from some of the best in the business. I'm a member & it's money well spent, IMHO!

Romance Writers of America: As soon as I can afford another membership, I'm joining RWA as well. They have fabulous resources and I've heard awesome things about their meetings & conferences & can't wait to be part of that community, too.