There are lots of initiatives that are popping up online to raise money in one form or another. If you do donate to a "flood auction" or similar initiative, ask for a copy of the receipt of donation. Make it Perfect are just one blog who is spearheading the online auctions held by handmade artists who have donated their stock towards raising money for flood effected people.
If you want to donate directly, the Queensland government has a site that lists all the donation methods.
It is worthwhile being mindful, that even though this event is horrific, most of the people in Queensland with the support of the nation will reclaim their houses, jobs and will get the best medical care that a first world can offer. Where as the 20 million people affected in Pakistan by the floods that happened in 2010 are still suffering from water born diseases, living in poverty and suffering from malnutrition.