I use the Domain car park pretty regularly, and it is in a very convenient location, and reasonably priced.
A couple of years ago it was a bit run down, but cheaper :-), The have since done it up with much better lighting, repainted it, and also updated the payment system, it used to be cash only, and now accepts credit cards.
There are heaps of spots, and you shouldnt have a problem getting a spot, when it is busy you might have to go down one level.
I like this car park too because of the really long escalator ride, it would be fun for kids as there are not many like this, and the wall are covered in artworks, though be warned that the escalator seems to be broken down quite often and its a bit of a hike.
Tips.....
Take your ticket with you, its a long walk to the payment booths!
Make sure that you pay for your parking on the way back to your car.
Remember where you park, as it has 3 sections that look similar. read more