Who do you think it is? Off the top of my head, I'm leaning towards Guy Pearce. Maybe Vernon Wells. Heath Ledger might have been up there eventually, but he's only had one standout movie (though admittedly I didn't watch the buttsex one).
Bryan Brown. He was excellent in fx: murder by illusion. Though he was actually pretty good in Breaker Morant. Or maybe Michael Caton. Gotta love The Castle In all likelihood it is really Geoffrey Rush by some considerable distance.
Bryan Brown is possibly my favourite although not sure where he would rank among some of the others, definitely up there though. This thread reminds me how disappointing Eric Bana's career has turned out thus far.
Guy Pearce is underrated. From the nerdy by the book detective in LA Confidential, to the smug count in Count of Monte Cristo, to the...main guy (I guess) from Memento.