Dean Wesley Smithhttp://www.deanwesleysmith.com/mt/
Dean is one of my fiction mentors. He has a forum section there where he answers questions about writing. He says he gets sort of blunt at times, and that's one of the reasons this site is always worth visiting.
There are a lot of posts that have discussions about different aspects of writing and selling and agents and just about everything anyone can think of to ask. No need to sign up. You can read it without doing that.
Chris YorkChris and her husband, J. Steven York, are two of my writing buddies up in Oregon. Their blog is posted irregularly, but always provocatively. Chris's latest post is on how writer's ought to behave at conventions—an essential read. http://cfyork.blogspot.com/
The London Times on Bestsellers and how they're promotedhttp://www.timesonline.co.uk/article/0,,1056-2202068,00.html
Mistakes Writers Makehttp://www.vickihinze.net/
Author Vicki Hinze's blog has a whole series of posts about mistakes writers make. Maybe you never believed there were so many.
Professor Paul Brians' (Washington State University) has a most useful online book, Common Errors in English <http://www.wsu.edu/~brians/errors/errors.html#errors> Using the reference, you'll never get wrack and rack confused, or prostate and prostrate, or literally hundreds of other common confusions.