There are several websites and blogs out there which provide concise, verified, useful information about the publishing business, and several more which send daily or weekly emails to their subscribers which are packed full of news about the publishing business. They're invaluable for writers, even those who aren't overly interested in the mechanics of publishing or in insider gossip.
I recognise that this is not an extensive list and it's very biased towards the UK, too: so I'd be very grateful if you could add recommendations of your own in the comments, complete with links and descriptions if possible so that I can edit them in here and build a really useful list. Thank you!
The fabulous AuthorScoop publishes a few posts each day, most of which are lists of links to publishing news and writing views. It's wonderful stuff and I'm very fond of it: if I'm not particularly disciplined AuthorScoop eats up whole days of my life.
BookBrunch sends out a good email roundup of publishing news and views daily, which is free: but if you want to read the full versions of each story on the BookBrunch website, you have to pay subscription fees.
Book2Book (also known as Booktrade Info) also rounds up publishing news stories and provides an email news service which anyone can subscribe to free of charge: unlike BookBrunch, however, Book2Book doesn't charge subscription fees to those who want to read the fuller story. Book2Book often links to publishing blogs: I've made their lists a few times now, and each time have enjoyed a very healthy boost to my viewing statistics as a result.
The Bookseller's website has a news section, a blog (which I've contributed to), job ads, rights sales, everything. It's sometimes criticised for being a little too staid but I don't think that's fair: it's thorough, demands meticulous, verifiable research from its contributors, and covers a lot of publishing ground. There is apparently an email update, which I have subscribed to but have never received. I don't think the problem lies with my spam-filter, but might well be wrong.
5th Estate is a blog written by editors, publishers and writers and is published by Press Books (a division of HarperCollins). It features book previews, opinion pieces and industry news, and, unlike some publishers' blogs, isn't wholly promotional.
Thanks to Victoria Strauss of Writer Beware! for providing me with the following links and information, which is mostly oriented toward the US market:
Publishers Lunch: For the "deluxe" version of this newsletter, you have to be a member of Publishers Marketplace, but the free version provides plenty of news and links.
Shelf Awareness is a free email newsletter for booksellers. It's bookstore-focused, but there are often fascinating tidbits of news here that you don't see elsewhere.
Publishers Weekly offers a number of free newsletters about the industry. I think you may need to be a PW subscriber to access these, though.
GalleyCat is a great resource for publishing news. You can also sign up for MediaBistro's Daily Media Newsfeed, which covers the media in general (not just publishing).