I have used this one: http://aquaticlifeaquariums.com.au/
and this one: http://www.aquariumproducts.com.au/
and have had no problems so far. I had something arrive broken in standard mail from aquariumproducts once but I complained and they gave me credit to the value of the damage item without even having to return it. It was only a $25 item but still.
All their prices are pretty good but I think aquaticlifeaquariums might have more range and some better quality stuff.
Peace.
I've bought from www.theaquariumshop.com.au twice. They have probably the lowest prices and they package everything really well. They mainly sell smaller, cheaper stuff (not the expensive top of the range items).
www.theaquariumshop.com.au is my favourite, my order was only 36 dollars, so i decided to go have a look in the lfs, the same stuff at the lfs would have costed me 78 dollars. and it was packed really great and arrived promply.