For me the first four pick themselves -
G.Chappell
Border
Waugh
Ponting
(even when you take into account the percieved weakness of opposition for Ponting compared to Chappell, Waugh (in the 90's) and Border I still believe he deserves a mention)
For the fifth position more than 10 names could be tossed about - Harvey, Simpson, Lawry, Walters, Hayden, Langer, O'Neil, Vic Trumper (for his status as somewhat of a pioneer of Aussie batsmanship more so than his numbers), Ponsford, Hassett, hell if you go by numbers even Martyn, Boon, Morris, Ian Chappell, Dean Jones, Mark Waugh would come into the equation.
I'll go for Harvey (even thought I dont like him!), for scoring over 20 hundreds in 79 tests before covered wickets were brought it.
Which makes my list identical to pretty much everyone elses lol