Australia Zoo, (Steve Irwin) is not far out of Brisbane worth a visit, the Lone Pine Koala Sanctuary, koalas and lots of other australian animals, is less than half an hour from the city. A ride down the Brisbane River is a nice way of spending a couple of hours. Moreton Island could be a good day trip and Fraser Island is fantastic though further away.
Brisbane is very hilly but there is a good public transportation system and it is very easy to get around. I spent four days there last year at the end of an extensive Oz trip and thoroughly enjoyed the place.