May I recommend WeWork Pyrmont?
Having bounced around a few offices in the city (started at Market Street, been in the Rocks, Surry Hills and now Sussex Street) I found WeWork Pyrmont to be rather nice, price wasn't too bad for the co-hab spaces (I ended up with a dedi-desk as I didn't fancy moving all my crap everyday in the freerange desks).
They have ping pong tables, lots of cool meeting rooms that scale to your needs and, oh yeah, free beer on tap..