I already new about Unshelved and Tales from the Slush Pile. Now I've learned about another whose posting isn't quite as regular, but it's still great: The Adventures of Comma Boy.
The first couple of strips are political, but once you get past them and get to the writing-related ones, particularly the ones about people preparing queries, it's hysterical and sounds like so many submission horror stories I've heard from agents and editors.
If you know of any other writing or publishing-related webcomics, let me know. I'm always up for adding to my list of ways to waste time on the internet.
Have a great week!