Voted for Melbourne, but I should’ve gone with Coober Pedy since it’s the best city name ever.
Brisbane, with Cairns in second place.
I used to have a pen pal in Collie.
Wagga Wagga is always the first one I think of.
I thought of a city not listed, Fremantle. I suppose the reason for that is the Tom Selleck movie Quigley Down Under. He landed at Fremantle.
Newcastle (for fairly obvious reasons).
Note that, strictly speaking, Canberra is not a city, even though most people think of it as a city, since it’s not incorporated as a city. Local government functions in Canberra are carried out by the Australian Capital Territory government.
Melbourne is usually the first city I think of, before Sydney even, as I have family there.
Pen pal too, when I was 11, in Perth. Wonder what happened to him. Pumpkin farmer? Eaten by dingoes?
Also, Perth Amboy, NJ, is only an hour away from me.
I thought of Ballarat. Probably only because it came up in conversation earlier this evening (yesterday evening now, I suppose).
Perth. Which I know nothing about.
There’s a few Dopers from Melbourne! We even did a Melbourne Dopefest way back in (errrr, maybe 2003??) Help me out here Eliahna! It was in a cafe at the corner of Brunswick St and Cecil St in Fitrzoy?? 
Anyway, I’m no longer a Melburnian, having moved a whole 100km away, so I now come under the jurisdiction of the biggest non-capital city in Australia, Geelong.
So, Geelong.
Oh, and just by-the-by, the Sunshine Coast and the Gold Coast are not cities, but ‘regions’.
Melbourne, because a big part of my company is there. But I would have assumed the popular answer would be Canberra, 'cos, you know, it’s the capital of the country.
Formula One fan here, so…
Cairns, followed by Alice Springs - which probably doesn’t count.
Ballarat was mentioned in a Sherlock Holmes story, “The Boscombe Valley Mystery”.
Melbourne, because that’s where Miss Fisher’s Murder Mysteries is set.
Oh, and also it’s where I live.
Melbourne, because I’ve known a few Aussies from there.
Half right: Gold Coast is in fact a city – the second-largest city in Australia, going on the population of local government areas, with the City of Brisbane being the largest.
Melbourne. Because I can literally see it from my back yard.