One of my favorite outside sources is Ruben Fletcher. His blog, Crack Skull Bob, is full of excellent sketches, and often his commentary is full of ironic humor.
Rubin has a sub-category of posts which he calls "Common Mistakes." It's a sort of advice-for-artists category with a surrealistic twist.
Here's my current favorite, with a spippet of the commentary:
You're drawing up a storm, in a crosshatching groove, and suddenly the whole thing comes down on you. It happens to experienced sketchers as well as novices....I love it.
Proper attention to drawing construction is what will prevent this tragedy from occurring. Add too much hatching to a flimsy structure, and you're just begging for trouble.