Hi Gail & John
You don't mention if you are taking kids so bit unsure on recommendations. If you have children, would def recommend the following.
Singapore: Night Safari; Sentosa Island (Swimming with the pink dolphins was a big hit); Raffles; Walk round the Esplanade, Duck Tour (kids loved it!)
Sydney: Trip up Pylon Tower on Bridge (couldn't do Bridge Climb as kids under 12); trip to Blue Mountains; Botanical Gardens,; Taronga Zoo; Manly on the ferry; Powerhouse Museum;
Brisbane: Southbank; Mooloolaba (1hr 10mins ish); Australia Zoo (1hr); Noosa (90mins ish!); Wet and Wild (1 hr); Sea World (1 hr); Sea cat Ferry trip up and down the river; Bike hire in the Botanical Gardens for half day;
The only place that we went that I def. wouldn't recommend is Surfers Paradise but that is only MY opinion, we were really disappointed with it so wouldn't go back. Everywhere else, we would def. go again.
A good website to also use is
Reviews of vacations, hotels, resorts, vacation and travel packages - TripAdvisor and go on the forums there. I practically lived on it when I was in the planning stage.
Good luck - Joanne X