If you want a city that is already built for you, I'd look at:
Freeport (piratey goodness, arrrggghhh!)
Bluffside (interesting premise, way cool, humoungous city)
Geanavue (beautifully done if you want a city that doesn't care for magic.)
Streets of Silver (think renaissance Italy, the Medicis the Borgias, poison, intrigue, and eeeevil.)
Seven Cities (generic, drop into any campaign, but not the most flavorful.)
I'm running a Freeport game right now, and I highly recommend it if you like pirates.
If you want to know how to build your own city, then you really must have Magical Medieval Society: Western Europe. Your next purchase should be Cityworks. Both of these are excellent resources for the city building DM. Plus they're fun to read!