I've been fortunate to have some old work suits that are still in fashion. For my dresses with belts, I love Review. I use a black office jacket to wear with the dresses from Portmans. I really love Review too for their dresses, and you can mix and match the belts. In fact, my profile photo was taken of me on the plane on a business trip, and I was wearing a Review dress. My jacket/blazer was hung up at the time.
Cue and Review are both perfect, and also for something a little bit different, I've recently discovered a store called Zeitgeist in the QVB. The clothes are colourful, fashion forward, and still mostly work appropriate.
I like to get basics (like pants or skirts) from places like Big W or Target. You can't tell where they're from just by looking at them, and cost a lot less than similar ones elsewhere. To mix it up I get other pieces from Myer, David Jones and Trade Secret. I've always been a fan of mixing cheap and luxe things together for a smart look that is still individual.