My Three
Cauldron from Dungeon magazine (issues 97, 98, 102, 104, 107, 109 & 111): It is a v.3.5 city for the contemporary D&D player and DM. It is very well developed, IMO. It has maps, a social structure, dungeons and compelling good guys and bad guys. Many of the city's key places and services are present with unique NPCs.
Hardby from Dungeon #109: It is v.3.5 like Cauldron. And, it is specifically set in D&D's default setting - the World of Greyhawk. I think Looby did a great job of bringing together the city's history and contemporary issues - complete with great NPCs and their affiliations and motives. Unlike Cauldron, Hardby is ready for any adventure. The bad guys are not so prominent, so the motivated GM can develop his or her direction for PCs in and around Hardby.
The Free City of Greyhawk: Well, this is the City of Greyhawk! It is enormous and very, very complex. It is also the cornerstone of the D&D default setting - the World of Greyhawk. I still use the 1989 boxed set, Greyhawk: Gem of the Flanaess, which includes adventure cards and two sourcebooks. I have also combined elements from the Living Greyhawk campaign, especially the nice, new map from LGJ#2. Many Core LG adventures have also developed and added to the Free City. AS noted above, you also have Anne Brown's Player's Guide to Greyhawk and Roger Moore's Greyhawk: The adventure Begins. The latter is still my favorite CoG product. The CoG has unlimited intrigue and adventure oppurtunites. It has so many "quarters," the PCs can find trouble in many different guises. So there are many resources for this bustling metropolis. I think the CoG is a DM's best friend for big-city adventure.
