Look Michael Clarke is the obvious candidate and I think he'd be a great captain.
But Katich would also be a good Test captain, and in the event that the selectors were desperate they might go to him.
Wait, what the hell am I typing? Ricky Ponting is going to be the Australian captain for as long as he wants to be. Yes, Hogg points out some of his more questionable decisions, but he's also done many good things and he's a pretty inspirational figure (I gather) based from the comments the other players make about him. I think he's done a fine job with the player turnover Australia has had to put up with.
At the moment, Ponting is a great OFF ground captain. Does media well, encourages and inspires the players in meetings and in training. So he runs the team well. It's on the field that he could improve a little. Sometimes he gets caught in a defensive rut with field placings and I particularly don't like the way he stares down umpires in the field, but that's a personal peeve, some quite like his intensity. With the on field stuff, I like the fact now that Michael Clarke stands with him in the slips a fair bit so they can chat about tactics (not recently though, it's been North and Watson at 1st and 3rd). It's when Hauritz comes on and they seperate that I get a bit worried about Ponting letting the game drift a bit. Clarke seems more aggressive in his instincts like a Shane Warne.
I might also add that Rodney Hogg is the kinda guy on a journalists speed dial. Someone's desperate for a story... Maybe tomorrow it'll be Jeff Thomson. Both are twits IMHO.