Will be in Brisbane the third week of March for business and then have six days free before go to Sydney. Where should I go? I thought of Cairns and GB; but worry about the wet season? Thought of Uluru but too touristy?

Just north of Bundaberg is Lady Musgrave Island. It is a terrific day trip from the town of 1770. It is the southern most Island of the GBR and has great snorkelling huge number of fish and coral.
http://www.lmcruises.com.au/

Going to Fraser Island for day trip (or longer) is worth while. As are the Glass House Mountains. We went with Hummer Tours (only takes four people)
http://fraserexperience.com/new/inde...d=15&Itemid=29

You can feed dolphins at Tin Can bay as well.
http://www.barnaclesdolphincentre.co...in_feeding.htm

We did all this easily in week last September.

Ayers Rock is fabulous although it will be very hot in March.

A six day dawdle down the coast to Sydney would be quite pleasant.

Welcome to Fodor's.

Uluru should be great at that time of year and not too many tourists yet.

You could take the dawdle to Sydney but it wont be so slow. There is a lot to see and do and you could do a little inland and some coastal touring, including wineries of the Hunter Valley. Unfortunately with the rise in popularity of Savignon-blanc, a lot of the regions semillion grapes are going into blends to stretch that variety.

Really no need to fly anywhere. Lots to see in southeast Queensland and nearby in northern New South Wales. Peter mentioned some great places north of the city. But there's more - west and south, the beautiful Border Ranges area (aka Gold Coast Hinterland) - lovely scenery, rainforests, waterfalls and wildlife - places like Springbrook, Lamington Nat'l Park, Mt Warning and Mt Tamborine. You could take these in while dawdling south to Sydney.

If you stay around Brisbane/South East Queensland, here are some links to places that are within a few hours driving distance (in some cases, ferry required)from Brisbane:
http://www.australiazoo.com.au/
http://www.sunshinecoast-australia.com/
http://stradbrokeisland.com/
http://www.moretonislandadventures.com.au/
http://nprsr.qld.gov.au/parks/glass-...ins/index.html
http://www.visitnoosa.com.au/

Thank you for all the great ideas!

There is flooding in Queensland now. There might be some lingering damage.
http://www.odt.co.nz/news/world/aust...ome-queensland