The first place to look is of course Homeone's very own homepage.
http://www.homeone.com.au/landscaping/
The next best place to start is by visiting your states Landscape association.
Why choose one of their members?
Well because these are businesses that actually care about standards and want to be pro active in making their industry better and better. They work to very high standards and are judged by their peers.
These sites will also contain loads of inspirational photos to get those creative brain cells into gear as well as assist in helping you choose a landscaper and or designer that stands out from the rest Have a squiz in the photo galleries and award sections.
Victoria... What am I doing? We will start with...
Western Australia
http://www.landscapewa.com.au/
Also we have the Western Australian Landscape Design Association
http://www.walda.com.au
The National Institute of Landscape Designers and Managers
http://www.aildm.com.au/content.cfm?id=876
Victoria
http://www.liav.com.au/
Tasmania
http://www.liat.net.au/profile.html
http://www.liat.net.au/member.html
South Australia
http://www.lasa.org.au/
New South Wales
http://www.lcansw.com.au/
Queensland
http://www.landscapequeensland.com.au/
Australia
http://www.landscapingaustralia.com.au/
New Zealand
http://www.lianz.org.nz/