For cars try the Europecar link of the Virgin Blue website. They have a higher daily mileage allowance and the best prices. That or Thrifty website direct and look for the special offers they have. These will only be out a few months. Remember fuel is a bit more pricey than the US so rent a smaller six or even a 4 cylinder if you can. The money you save on gas can easily be spent somewhere more fun.

www.virginblue.com.au/