Highlights of Brisbane?

Go on the CityCats (the local ferries) which go up and down the Brisbane River. You can get on and off but the whole trip alone takes about 2 hours. You can get to a few things on the City Cats. New Farm Park is nice for example and you could check out restaurants and shops within a short walk or enjoy a picnic. South Bank area is good (more on that later).

Might I suggest buying Go-Card each if you are wanting to use public transport (eg Brisbane City Council and some other buses, trains, ferries). Website attached below and use translink to view timetables etc. It will just make fares a little cheaper (maybe as much as 1/2 price), and you can get quite a long way with them (Gold and Sunshine Coast, Ipswich). They cost about $10 to buy including the same amount of credit loaded on already, and you can top up small amounts say $10 or $20 to get you through. Then just run them down to as low as you can go before you leave. Just remember to scan them on at the beginning of the journey and off at the end of each journey (a journey is each segment so on a train and a bus, scan on at the begining of the train journey then off at the end, on at the beginning of the bus and then off again.

Southbank area. Southbank itself is lovely with walking (bike / rollerblading) tracks along the river and through rainforest areas. There is a swimming beach. There are also plenty of restaurants and cafes and eateries both in Southbank proper and all around the area. On the weekends (Friday night and Saturday / Sunday) there are markets.

At one end of Southbank there is the Cultural Centre comprising of the Queensland Performing Arts Complex (QPAC) which has 2 larger stages (about 2000 seats), 1 mid size (nearer 1000) and one small performance area. There are things on so maybe see if there's a show on if you are interested. Also contains the Queensland Museum (currently under refurbishments and will open January 2012), Queensland Library and two seperate buildings of the Queensland Art Gallery and Gallery of Modern Art. The performances at QPAC do cost although they do have some freebies. For the rest, they are free mostly except some travelling exhibits do attract small costs (about $20) for an adult ticket) but you get movies and talks to go with that.

Westy End which is just beyond Southbank / South Brisbane and has some great eateries.

Lone Pine Koala Sanctuary is nice if you are from overseas and want to see / touch Australian animals. It's about a half day trip rather than a full day

Roma Street Parklands and the Brisbane Botanical Gardens are a nice walk around and they can be walked to too, check out the living heritage site below for some ideas

The Mt Coot-tha Botanical Gardens and lookout (seperate) are worth checking out too.

You can also go further afield to places like the theme parks on the Gold Coast like Movie, Sea or Dream World. You can get on the train / bus down. It will take longer but you don't have to worry about traffic and parking. Entry costs will be high and the whole day with food and stuff may be more than a $150. However other days (eg a day on the City Cats and a day wandering Southbank) will cost you transport and food and maybe a little more but shouldn't be expensive...

Up the Sunshine Coast there is Australia Zoo and Underwater World