King Neptune,
My diving has been a 60/40 split between Cairns/Brisbane, here the diving tends to be quite seasonal exspecially in Brisbane for example currently there are a lot of Grey Nurse Sharks (Sand Tigers) around which make for some great diving, only 3-4 weeks back I dove with 11 of the buggers, and then had the pleasure of seeing humpback whales breaching during the surface interval.
At other times of the year Mantas are common off of Brisbane, aswell as all the usual tropical/sub tropical marine life.
Spots up off of Northern Queensland Coast have a lot of Seasnakes, Bullrays, Sharks and huge Queensland Gropers (I would imagine it was one of these that a persons head was found in earlier this week off Townsville), and of course beautiful reefs, currently though there is quite a lot of damage being done to some of the reefs off Cairns both by the huge amount of tourists and the crown of thorns, so when you do eventually make it over here it is well worth making the effort to go to some of the more out of the way places. Top spots include - The Ribbon Reefs/Coral Sea, The Yongala, Heron Island and plenty of spots of Moreton Island.
Anyway thats enough from me my fingers are starting to go numb
Cheers
Dez