Not all of them make it down to Australia - or, at least, not on free to air television, anyway. But, I've had some exposure to most of them.
Craig Ferguson and Conan O'Brien are my favourites, though I can't give any real reason other than the fact that their style of humour just matches up with mine. Jay Leno - well, I have no idea what he does that makes him so popular, but at least he's inoffensive. David Letterman annoys me, though.
Any others floating around haven't really made enough of an impression down here for me to have an opinion.