Try these:
http://www.meritonapartments.com.au/
http://www.rentahome.com.au/
Me and other FTers stayed at the Meriton World Tower, though it seems like it was less of a deal than for MG last year. The price has since doubled for their 3 bedroom units. I took a quick glance at rentahome.com.au, and they seemed to have a much more varied selection of properties at much more reasonable rates than the Meriton. However I have no experience booking through them.
Oh, and if you're really looking for something over the top for you and a smaller group of friends, there's always the
Moog Hotel.