I have used

bitinnovate.com (suspended trading now) - took less than 4 hours for coins to arrive in my wallet

spendbitcoins.com - great took less than 2 hours to arrive in my wallet

MtGox - after approval wire transferred money took 7 days too slow

I use the following exchanges
BTC-e
Cryptsy
MtGox
Vircuex

BTC-e has so far been the favorite

I use Mtgox for withdrawls into AUD as they are the only ones who I have found you can setup an Australian bank with (have not tested withdrawl yet as love my bitcoins)

So basically
Buy bitcoins from spendbitcoins and send to your online wallet at the exchange of your choice.
Setup approved banking with mtgox so you have option for withdrawl into your Australian bank account.
Send coins to mtgox when you want to withdraw if you use a separate exchange.

hope this helps for all you aussies.