I almost missed this, stumbling upon it while browsing the Wizards forums while trying to avoid the constant salvo of crap and misconceptions being thrown about, which would have been a shame since its a very crunchy article and my wizard can almost use some stuff out of here...
Secrets of the City Entombed is an article made up of background and mechanics in about equal measure. It opens up with a description of the city Rahesh, a place where the dead walk and are probably smarter than the politicians. Unless they were politicians in life, that is. It quickly wraps up with a section on the Scholars of Sin, as well as some Arcana and History DCs to see how much you know about the place before quickly moving on to the good stuff.
The name of the theme is necromancy, and I know a lot of people were chomping at the bits for this. The last half of the article is devoted to providing new powers for the avenger, bard, cleric, shaman, swordmage, warlock, and wizard. Thats right, well before PH2 is even out we're already getting support for some of the new classes. More than a few of the powers have the Summoning keyword, which is explained in a very nifty sidebar.
Of particular interest is the animate dead spell, which weighs in as a level 9 daily that lets you raise any dead monster to kick ass on your behalf (and standard actions). While they share the same set of stats, its more of an aesthetics part that gives it that cool factor.
This is certainly one of the best articles released so far. It covers a wide range of classes with some solid powers that I think a lot of players are going to enjoy.