Like Vancouver BC, Seattle is also “Rain City.” (According to local three-dot columnist Clark Humphrey, “Emerald City” is a 1980s-era chamber-of-commerce neologism that we newcomers have been duped into using unironically.)
Another one is Lotus Land.
And Douglas Coupland is absolutely right that Vancouver is never just Van. I have a former co-worker here in Victoria who always referred to Van., and it made me cringe every single time.
Wasn’t Petaluma, California, once called Chickaluma for its poultry farms?
A few from the LA area:
Long Beach: The International City
Compton: The Hub City
Lakewood: Tomorrow’s City Today
Culver City: The Movieland Capital, or something like that
Colton: Hub of Industry
I don’t know if Santa Monica has an official nickname, but it is known locally as The Peoples’ Republic for its lefty views.
My city’s nickname is Dullsville, though it’s not dull as much as it is empty. It is also the most isolated capital city in the world.
Glasgow (Scotland) The Granite City or Knuckle Butty Town
Macclesfield (England) Silk Town
Manchester (England) Cotton City
Oldham (England) Milltown
Leeds (England) Jeezwhatadumpthisplaceistown
Actually, it wouldn’t surprise me if residents of King County came up with that pejorative – Tacoma is in Pierce County. 
Long Beach, CA - Used to be known as “Iowa By The Sea”, because of a large number of midwestern settlers.
Cincinnati has also gotten “The Nasty 'Nati” from it’s less than enthused inhabitants.
Lake Placid, FL is called both “The Caladium Capital of the World” and “The City of Murals”, on the rare occasion that anyone calls it anything. 1700 people in the middle of nowhere, but they’re responsible for 95% of the world’s caladium crop.
Another one for Orlando is “The City Beautiful”, but that’s total bullshit.
Tampa is “Cigar City”, and the entire Tampa Bay area is the center of the Suncoast. However, while I can think of names for some neighborhoods in the area, none of the cities have nicknames.
Tampa is The Big Guava.
Atlanta is also sometimes billed as “The city in a forest.” I kinda like that one.
And back in the Civil Rights era as “The city too busy to hate.”
Boise, Idaho is called Bobo by many of the older generation of locals and “Northenders”. Most people however, know the nickname promoted by the city officials, “The City of Trees.”
I’ve heard Houston referred to as ‘H-Town’ and ‘The Seattle of the Southwest’. The second one makes sense b/c once it does start raining, it doesn’t stop. Also over the years, heard it called ‘The San Francisco of the Southwest’, even pre our mayor. It depends on what you read.
Rome, the Eternal City.
I’ve always thought “Chi-town” was pronounced “Chai-town.”
To me, Milwaukee will always be Beerfart, WI.
Oslo, Norway is “City of Tigers”.
Austin, Tx : BatCity, City of the Violet Crown, Republic of Austin, Live Music Capitol of the World
Corpus Christi, Tx: Sparkling City by the Sea
Eagle Pass, Tx: Where Yeehaw meets Ole
El Paso, Tx: El Chuco, Sun City
San Antonio, Tx: River City, Alamo City
My home town, Camarillo California: Lima Bean Capital of the World. I now live in Campbell, California, which is the Prune Capital of the World. Yay for fiber, I guess.
Calgary is also known as Sandstone City. And, as my husband points out, “The Heart of the New West,” which I don’t think anyone has ever called it in real life.
Lethbridge, Alberta is also known as LA, which is funny, because the population is about 83,500. 
Another one from the LA area: Lomita: Celery capital of the world