...of course I'm most intrigued by "Cellar." I started out in SL after a friend of mine started building Silent Hill replicas, which I remain convinced were probably the first urban decay sites on SL. I've been drawn to the gritty, dirty places ever since.
Explored Cellar a little bit a couple weeks back... poseballs aside, it IS a beautiful build, especially in Windlight. It's a shame it went the direction it did.
That said, i'm not sure where i came across it, but I saw an ad for http://www.thecrackden.com/ today, which seems to promote more of the urban decay aesthetic, in the form of both commercial and residential sims. I'll have to check it out when I get home later.