Cape Town’s official nickname is The Mother City, due in part to Cape Town being SA’s 1st city. The unofficial one is Slaapstad, which literaly means Sleep Town in Afrikaans (Cape Town is Kaapstad in Afrikaans), because we are seen as being very laid back and spaced out.
Now in Cincinnati, with a few of nicknames:
[ul]
[li]Porkopolis[/li][li]The Queen City[/li][li]The 'Nati[/li][/ul]
Used to live in Frankfurt on Main, which was nicknamed “Mainhattan” because of the (unusual for Europe) tall buildings.
Someone previously stated I am in “South Cakilaki” and I had to guffaw at this…haven’t heard someone say that in a long time!! I am in Charleston, which is nicknamed “the lowcountry.”
Hell’s Kitchen, part of The Big Apple.
Umm… Sydney is known to the locals as aah… Sydney.
If you know a little about Aussie culture, you’ll know that Sydney is considered the glitzy, entrepreneurial, brash in-your-face city, compared to Melbourne being the leafy, cultured, old school tie, old money, boulevarded one. We’re kinda LA to Melbourne’s Boston. To this end, the Melburnians call us “Tinseltown” or “Sin City”, both of which are appropriate. We call Melbourne (when we think of Melbourne at all) “Bleak City”, which is probably a bit harsh, but apt in some ways.
Why not just Brissie? 
Auckland is “The City of Sails”. Yep, the marketing gurus have had their way, and now th’ ordinary Joe and Jane Kiwi born north of the Bombay Hills uses that nickname.
“The Ski Capitol of the East”
Also known as Snob City.
I live in Florida’s armpit.
Also, my state is ‘The Nation’s Wang’.
Some locals have taken to calling our fair city ‘Shelbyville’ after the ridiculous constitutional amendment from the 2000 election.
Viva, Greenvegas!
I live near Portsmouth (UK) which has a long tradition of being calle Pompey. (‘pom-pea’ not Pompeii)
Indy
India-no-place.
“The biggest one-horse town in the world”
Circle City
Guess which one the Chamber of Commerce prefers.
There was a daffy marketing attempt to use “Little Apple”, some years ago, but it was ignored.
NOVA
“No, that’s West Virginia”
“Wannabe Silicon Valley that never really was even close because everything here is just one tiny shard above mediocrity yet nobody seems to know that.” <— Well, I made that one up by myself No, really, I like it here.
And I’ve never lived in these Virginia cities, but when I used to have to go there for work a lot.
Manassas : “Manasshole”
Culpeper : “Culpecker” (weren’t we creative)
Phoenix, where I have lived far too long, is nicknamed
“The Valley of the Sun”
or, as some astute fellers have taken to calling it,
“The Valley of the Sunstroke”
I believe I have referred to it as varying levels of hell before too. People should not live in a place that hits above 120 degrees F.
Come to think of it, I can’t think of any for San Francisco besides “Frisco.”
However, that won’t stop me from calling that other town Hell-A. 
::glares at Troy McClure SF::
Manchester NH is known as ManchVegas.
The only explanation I’ve heard is that at night, from the surrounding hills the lights look a bit like Las Vegas (being the only urban area in sight). Maybe something to do with the nightlife too (not that there are a lot of bars for one city, just that its the only largish city around).
Someone will have more interesting things to say about where I live now, New York City, so here are some for my hometown of Buffalo, NY:
The Queen City
What a yawn, so we’re what, one of hundreds of cities that thinks its nickname is “the Queen City”?
The Wings Capital of the World
Well yeah, I guess that’s true, but no one walks around using it in conversation.
The City of Good Neighbors
That must have been some city council meeting when that one was thought up. Again, can’t imagine an actual person using that nickname in actual conversation.
The Nickel City
This one is the only one that has some potential for being cool. FYI the US five cent piece used to have a buffalo on its tail side, so Buffalo became the Nickel City.
L.A. - lower Antioch (Antioch being a Southside suburb of Nashville).
Supposedly a “tough” neighborhood but I’ve never quite got it (10 years now) but I did grow up in E. Atlanta so maybe that explains it (?).
I was born and raised in “Hawkeye-ville”… or “Corn Country”… or “Is this Heaven…?”