It’s the Internet, so I shouldn’t be surprised when I find an excellent list of reference/style/grammar sites for writers on a design blog.
Still, I’ve been looking for a chance to mention the Designers Who Blog site for ages. Despite the title, they also concern themselves with photography, advertising, writing, etc.
Stop by and kick the tires.
As for the list of links below, it’s a real grab bag. But it includes some hugely useful stuff.
Bookmark it, tag it, copy it – just make sure you’ve got it.