I have a few domain names, and a couple of sites. I have one name registered with an Aussie provider, and the other with US providers. I have one site hosted by an Aussie service, and the other hosted in the US. I've had these, and a few sites before, for around 8 years.
Aussie providers will always cost more, for both domain registration and hosting. I personally think it's better to have a .com rather than a .com.au .
I'll soon be changing my remaining Aussie stuff over to the US provider as the value is magnitudes better.
In the US I use GoDaddy
http://www.godaddy.com
Cheers,
Jason.