Hi Grant,
I know this is going to sound biased (since I am from Victoria), but I think you should come to Victoria for your holiday.
The following is a must see and do list of all the things Melbourne, and the broader state of Victoria has to offer (well the majority of things to do)
The Royal Melbourne Zoo http://www.zoo.org.au/MelbourneZoo
Werribee Open Range Zoo http://www.zoo.org.au/WerribeeOpenRangeZ...
Healesville Sanctuary http://www.zoo.org.au/HealesvilleSanctua...
Melbourne Aquarium http://www.melbourneaquarium.com.au/
Melbourne Museum http://museumvictoria.com.au/MelbourneMu...
National Gallery of Victoria http://www.ngv.vic.gov.au
The State Library of Victoria http://www.slv.vic.gov.au
Luna Park http://www.lunapark.com.au/
Puffing Billy http://www.puffingbilly.com.au/
Fairy Park in Anakie http://www.fairypark.com/
Queen Victoria Market (weekend market)http://www.qvm.com.au/home.php
Scienceworks http://museumvictoria.com.au/Sciencework...
Melbourne Observation Deck http://www.melbournedeck.com.au/
Eureka Tower http://www.eurekatower.com.au
Eureka SkyDeck http://www.eurekalookout.com.au
Rialto http://www.rialto.com.au/
Sovereign Hill http://www.sovereignhill.com.au/
The Old Melbourne Gaol (have a self guided tour or for something more scary go on a night tour (tickets fort this can be bought from ticketek 13 28 49 ) http://www.oldmelbournegaol.com.au
Federation Square http://www.fedsquare.com
You also gotta go to Phillip Island and check out the Penguin Parade. While in Phillip Island go to Amaze 'n' Things http://www.amazenthings.com.au/
If you are hanging out to do some shopping whilst in Melbourne, not only can you find some bargains at the Queen Victoria Market, but DFO have heaps of designer brands at bargain prices, so you gotta check that out too. http://www.dfo.com.au
Don't forget to go down to Lygon Street for a bite to eat (there are heaps of Italian restaurants and there is an ice cream shop there (sorry I forgot the name of it) where they sell the best ice cream in Melbourne)
If cakes and pastries are more to your liking, then a definate place you gotta check out is Acland Street in St Kilda. This is a street filled with the best cakes and pastries in Melbourne.
Chinatown is also a place you should check out if you are into Chinese cuisine. Not only this, but you can also go to the Chinese museum, and participate in a Chinatown heritage walk http://www.chinatownmelbourne.com.au/
If you are after a unique dining experience, why don't you try Hard Rock Cafe http://www.hardrockcafe.com.au and T.G.I . Fridays http://www.tgifridays.com.au
For a real memorable dining experience, spend the night at the Titanic Theatre Restaurant in Williamstown (this is worth the money you pay) http://www.titanic.com.au/html/home.html or the Colonial tramcar restaurant http://www.tramrestaurant.com.au/
You can also grab a bite to eat as well as a floorshow at the many theatre restaurants located in and around the city such as Dracula's and Witches in Britches just to name a few.
If you feel in the mood for some serious gambling (its your choice), the place to go is Crown Casino. At Crown you can also grab a bite to eat at any of their 40 restaurants, cafes or snack bars, take in a movie at Village Cinema which is located inside Crown Casino, play ten pin bowling at King Pin bowling lounge, play interactive games at Galactic Circus, dance the night away at Fusion and Club Odeon nightclubs or just SHOP, SHOP, SHOP at exclusive designer boutiques such as Versace, Louis Vuitton or Prada just to name a few and other general fashion stores http://www.crowncasino.com.au/
Victoria can be called the sporting capital of Australia as it holds the Melbourne Cup (don't forget to go to one of the weekly race meets at either Flemington, Caulfield
or Moonee Valley while you are in Melbourne), The AFL Grand Final, The Australian Open, The Australian Formula 1 Grand Prix at Albert Park and the MotoGP at Phillip Island just to name a few sporting events.
You can also find out of things to see and do at Docklands and Waterfront http://www.docklands.com
There are plenty of other things that you can do while in Victoria, just go to the visit victoria website for more details http://www.visitvictoria.com.au or http://www.thatsmelbourne.com.au (that sounded like an advertisement just then * ha ha*)
Enjoy your stay in Melbourne and have lots of fun!!!!