Paypal

When you go to buy something with USD through Paypal in Australia, Paypal will helpfully offer to do the currency conversion for you and let you pay in AUD. At least with my card, even if I do this I'm still charged an "Intl Visa Fee", presumably because Paypal isn't an Australian company. Paypal will also charge you a 4% currency conversion fee. For all I know other people are being charged exorbitant fees by their own cards but only when they're paying for things in USD, which would make Paypal's offer worth it - but at least for me, taking it up means I have to pay twice (and Paypal gets 4% of the amount I paid for offering no useful service at all). Obviously you should work out how the fees work for you before making any sort of large international purchase, unless you really want to give paypal a cut...

^