Poets & Writers Magazine - The magazine that covers all things publishing. Find out about MFA programs, read agent and author interviews, keep a list of upcoming contests and deadlines. Check out the Connect With Others section of their website- you can ask questions and vent your writing-related frustrations on their Speakesy message forum.
Writers' Market Series - Writers Digest publishes these huge compendiums that include lists of agents, how to query, places to submit. You can get books specifically on poetry, novels and short stories, agents, and children's literature. If you're fed up with clicking around from website to website and keeping your own lists of where to submit, these books are for you.
Nonfiction writers, check out The Situation and the Story by Vivian Gornick, which focuses on the art of the personal essay. Tell It Slant by Brenda Miller is a great craft-oriented book for the creative nonfiction writer. Fiction writers looking to generate new material check out, Now Write! which offers prompts from writing teachers. And those interested in poetry, have you read Mary Oliver's A Poetry Handbook? In this book Mary Oliver not only teaches you about rhyme and meter but she also teaches you how to read poetry. Even for fiction and nonfiction writers, this is a great book that helps you understand the power of rhythmic language.
And the one thing we said over and over again - read! Actually, William Faulkner says it best.
“Read, read, read. Read everything -- trash, classics, good and bad, and see how they do it. Just like a carpenter who works as an apprentice and studies the master. Read! You'll absorb it. Then write. If it's good, you'll find out. If it's not, throw it out of the window.”