This 2010 document by the Australian Automobile Association (AAA)
lists those countries where an International Driver's License is "required"
and those where it is only "recommended".
See
http://www.mynrma.com.au/media/AAA_Handbook_Jun.pdf
Though the US Embassy in Canberra web site in its advice to
Australian visitors states "Some rental car agencies require an
international driver’s license as part of the agreement", as others
have anecdotally noted in this thread, I haven't been
asked for one there in recent years.
See
http://canberra.usembassy.gov/resour...l.html#license
Back in the day when Australian driver's licenses just being folded pieces
of paper with no photo ID, US rental companies may have asked for them then but I have
no immediate recollection. Many bars in the US require you to show a
driver's license for ID as a condition of entry and I recollect back in the
80's you would get a puzzled look from the person on the door when you
handed them a paper license with no photo on it and in the case of the
New South Wales license, not even the word "Australia" appeared on it
anywhere.
These days with the photo licenses and combined with the fact they are
in English, it is probably rare to be asked for one in the US. I rented
a car there last month and it was not a requirement to have one.
Last month I also rented a car in Cuba and though the national language
is Spanish, a NSW photo ID license, a passport and a credit card from a
non-US bank was all that was required to be given the keys to a car from
one of the state-owned companies.
In Australia, third party personal injury insurance is compulsory and you
cannot register a vehicle without it. Take note that in the United States
that the rental vehicle you hire may not have any inherent or adequate
third party personal injury insurance without taking out additional insurance.
Rental car insurance in the United States is a confusing area, For example,
this page is produced by Hertz and there is a dizzying array of acronyms -
https://www.hertz.com/rentacar/produ...ctedAreYou.jsp
Think in terms of the liability involved in injuring a high-paid Hollywood actor
and their lawyer as a benchmark for the types of coverage that may be required.