Thanks to everyone for the continuing great entries, I'm glad the topic has sparked your imaginations!
Whether it's a fictional ideal city, fictionalized versions of real-life cities (Blade Runner's LA, Tokyo in either Yakuza games Tokyo 42), cities full of crime like Khare from the Sorcery! games or Batman's/Burton's Gotham, the comfy atmosphere in Hobbiton, Pallet Town, Celadon city and Whoville, or Raccoon City and Midgar suffering under the results of their rule by Umbrella and Shinra - they're all memorable places.
cose_vecchie: Thanks to DiffuseReflection for the giveaway, and congrats to the winner! For what it's worth, I'd like to add that "The City" from the Thief series is also one of my favourite settings from one my favourite franchises of all time, so eerie and unsettling with its mix of magic and technology, and so rich in atmosphere and lore.
And then Rapture, a wonderfully original, highly detailed and fertile setting, with the contrast between its past
Art Deco splendours and its present of madness, rotting and decadence. Coincidentally, I am playing and hugely enjoying Bioshock 2 at the moment, after having loved the first one. I think they're great, just like the Thief games.
Let me end with another fictional city that I had initially considered submitting for the giveaway:
"La Citta' Ideale" is a well-known Renaissance painting from the end of the 15th century, currently in Urbino. A vision of pure order and beauty. It's not the only one of its kind but it's probably the most famous. The author is unknown, though.
PS
I also thought of
Khare', the "Cityport of Traps" from the
second book of Steve Jackson's "Sorcery!" series, since I am a collector - and (very) occasionally a reader/player - of gamebooks.
Good news: thraxman decided not to want the Oblivion key after all. Therefore I will choose to give it to the runner-up, and it is you,
cose_vecchie for your original entry of Gilles Tréhin's Urville. Congratulations! I will send you the code in chat.
By the way, La Citta' Ideale is a beautiful painting and a nice use of symmetry and perspective, but why does the ideal city not seem to contain any people? :-)