THe best city adventures I've found ar ethe actual city books. Bluffside, Freeport, City State of the Invicible Overlord....all these books have great adventiure seeds in them but the DM does have to flesh them out a bit. THe great thing though is they will be good for more then one adventuire plot.
I'll second Bluffside. I got this as a free PDF from somewhere (sorry, can't remember where ), and now I wonder why I never bought it in the first place! 180 pages of a great city setting should let you find something good.