Big City Books?

[Whizbang Dustyboots]

While not a city per-se, Redhurst: Academy of Magic, is supposed to be great. You can find more info here. I'd also recommend Bluffside and Freeport.

Redhurst actually functions pretty closely to a Sigil-style city, but on the small town scale. It's a great, great book.

 

[ColonelHardisson]

If you could find them, the long out-of-print Town of Baldemar (a systemless, or perhaps a better way to put it is all-systems, product) and the Free City of Haven are outstanding.

ICE produced a couple of nifty city books, Minas Tirith and Minas Ithil. Both are fairly easy to saw the serial numbers off of.

Others have mentioned Bluffside and Hollowfaust, so I'll just second their mentions.

The Game Mechanics are producing the "City Quarters" products. So far, they have the thieves and clerics quarters. Both are pretty cool, and can be plugged into just about setting. Hopefully they'll complete the line.

 

[JoeGKushner]

Yeah, the Game Mechanics little city is coming along quite nicely. I really need to write a review of that divine quarter bit. Hope that they do arcane quarter next!

 

[Hand of Evil]

AEG's DM Toolbox - while not a city book, it is a book of tables that allows you ti fill in your cities with just about everything.

Bluffside and Streets of Sliver are two standouts.