I usually go with http://www.travelinsurancedirect.com.au/
They're cheap, offer coverage to suit my needs and their customer service is good. I've never made a claim with them though.
I have, however, made claims with STA Travel Insurance and Cover More (Flight Centre). Both were excellent in regards to the claim, however they do cost much more than Travel Insurance Direct.
Check the exclusions if you're going to do some activities that the insurers may consider risky, like skiing or rafting. Also, be aware that sometimes hiring a bike or a boat (for example) might not be covered.
IMHO the health cover always seems rather generous, even on the cheap cover, so I never bothered getting higher cover. I usually just get the cheapest I can for NZ, making sure that it would cover the excess on the vehicle I was hiring.