If you like business areas and very...precise living, check out Frankfurt. Turin is pretty interesting because it is so high up and quite a large city. If you've been to NYC and liked it you should have fun in London. If you like art, Paris and much of Italy are necessary. If you like history...Rome and certain cites within Greece are musts. There are so many nice cities in Europe that are really quite unique, you're just going to have to weigh out your enjoyment on a time/fun economic basis.
What you should check out is which regions or cities have special events going on during that time... cultural things, you know.
any budget or travelling constraints? what languages are you familiar with? certain places are more english-friendly, keep in mind.
ps I'm not sure how it is with australians, but eastern european and scandanavian women especially like american men moreso than the rest of European women hahah
