The Cult of Cartman: Revelations. Very intrigued, I was. And while I am sure that this set is a spoof of the X-Files Revelations DVD set, I find this one particularily original and interesting. I will not bother to list the episodes in this set, since previous reviews include them already, though I will mention that some of these episodes are by far among the best South Park has to offer (Awesome-O, Super Fun Time, Eek A P**** and the two-parter Cartoon Wars). In addition to this, the box is designed to look like a book (Revelations, after all) and you get an Eric Theodore Cartman Society membership card (which expires in 2012, along with the rest of civilisations) and a nice sticker. And on top of that, each episode is introduced by a life lesson by Eric Cartman, which is very nice any funny ("Never take a joke too far, Hitler learned this one the hard way" would be an exemple of that).
Obviously, these are not good enough reasons to buy this set if you already have the season sets, since the card and sticker are negligable and the Life lessons by Eric Cartman will make their way to youtube soon. But being someone who does not want to spend too much money on one show (given the fact that I watch a lot of shows), I am more than satisfied with what this set has to offer.