I've always liked this cover gimmick and if I had more time and money, I think I'd like to track down a complete set. In some cases, they break the fourth wall, while in other cases they simply add to the feeling of suspense.
Let's start with the most well known example. Brave and Bold #124 is a standout issue from a standout series. Artist Jim Aparo got the enviable task of doing a self-portrait on a comic book cover. This story is about as off the wall as Bob Haney ever got (and that's saying quite a lot). Haney, Aparo and editor Murray Boltinoff all play a role in this story that really has to be read to be believed. Bob Haney certainly paved the way for the likes of Grant Morrison. Like all Aparo covers, it is beautifully designed and executed. Even the fake cover he's drawing on this cover is top notch. If you don't own this book, do yourself a favour and track it down.
Next up is the rather notorious cover to Punch Comics #9, published by Harry 'A' Chesler in July of 1944. Chesler comics often featured incredible covers and less than incredible interiors and although I've never read this book, I can only assume it fits the mold. Paul Gattuso did many of the covers for this series, but I don't think this is his work. Anyone know for sure? The fact that this artist was killed might explain why this title never had issues #3 through #8 and had a hiatus of more than two years. It would be particularly cool if the cast of murderers on the cover were featured in this stories within. This cover is a beautiful and gory mess.
Every since I was a child, I have admired the cover to Tales of the Unexpected #1 from February-March, 1956. I believe that it was featured in the cover gallery of the first Overstreet Guide I ever owned (circa 1983) and it has always stuck in my head. This one features the 'creation come to life' angle, as the artist is confronted with a full colour version of his winged demon. I'm not sure exactly why a green guy with angel wings in purple pajamas constitutes a 'Dragon Man', but who am I to argue with the logic of DC in the 50s. Bill Ely isn't exactly a name you hear very often when great artists are mentioned, but he did a very nice job here on this Code-friendly classic cover.
Another subcategory of the Terror at the Drawing Board genre are those covers with a voyeuristic feel. Dick Giordano's cover for Unusual Tales #13 (September, 1958) is a perfect example. This one has a very creepy vibe to it, as an alien creature peers at the artist through a skylight. This design conveys a real sense of vulnerability - one of the keys to making horror/suspense work in my opinion. I'm not sure if this alien is the creation of the artist, or whether he doing sketches based on reports or sightings. This one is subtle, yet very effective. It was re-used 25 years later for Scary Tales #41, although I much prefer the original colouring job.
Finally, we've got the Gil Kane pencilled cover to Big Town #19 (January-February, 1953). I love this one because it is so ludicrous. What kind of a thug can't even come up with his own plan to kill Wilson? Why would these guys want to leave a paper trail of cartoons? You've got to think that Haney had this one in mind when he came up with Brave and Bold #124. I've only ever owned one issue from this series, but I'd certainly pick up more if the price was right as the covers totally suck me in. The 'Cartoon Crimes' story is apparently drawn by Manny Stallman, so that really seals the deal for me. I need this book.