Well I actually know a lot about Australia, so I do have a few thoughts on this.
First, I'd try to find a cookbook that has both U.S. Standard and Metric -- and, if you can find it, British Imperial. If not, maybe print out a conversion chart from the Internet and insert it in the book. In Australia, they use a combination of British and Metric, so it's important for them to realize that, for example, our cup is 8 oz, while theirs will be 10 oz.
Asia is almost spitting distance from Oz, so the country was inundated with great Asian food long before the first Mexican place popped up. (On my first trip down, 20 years ago, every shopping mall had a food court with Malaysian, Cambodian, Vietnamese, and Indonesian food, and you could even find street vendors selling hot goat curry or grilled octopus). So I'm thinking Rick Bayless would be a much better choice than, say, anything from Asia (though Indian cuisine is not an overwhelming presence in Australia, like SE Asian is). They may have Mexican restaurants now, but it's not ingrained, like it is here. So any of Bayless's books are a good idea.
Anything North American is cool, in fact -- Cajun, Creole, Southwest classics, New England, Old South -- stuff that is present to some degree but less familiar.
There was a huge influx from Europe after World War II (for example, Melbourne has the third largest Greek-speaking community in the world, after Athens and Thessolonica), so most of Europe is well represented, both in restaurants and cookbooks.
So my top recommendations would probably be to go with the Bayless and (depending on how many books you're sending) some other North American regional cuisines, and maybe dip into something nouveau or artistic -- not a particular ethnicity, but just something that makes your mouth water.