I was browsing the various webcomics and blogs I read when I stumbled across the Lost World of Warcraft site. I'm sure it's not new to a great many of you, and the information may not be earth-shakingly current, but the ease of having it all in one place to browse and the neat graphics available meant that I spent a while browsing it. I especially enjoyed looking over the Azshara Crater entry, since that's one of my favorite bits of speculation. I still think they should either make it a 25 man PvP battleground (since 25 is the new 40) or a raid instance zone similar to the CoT version of Mount Hyjal.
The site's a little behind the times (it seems to have stopped updating around the time TBC was in beta) but it's still a solid little snapshot of places that never got off the ground or which ended up removed or never intended for player consumption. I've flown over Elwynn Falls a whole lot of times and never even noticed that cabin.
So if you're interested in this kind of 'secret cow level' stuff, check it out. And if you can think of any places the site's missed, I'd like to know about them.