I can only say Melbourne clubs because I've never travelled. But this thread is great because I'm trying to plan a party trip for later this year.
In Melbourne, (Depending what music and atmosphere your after), the best all around club I think is Billboards. It has really nice Vj antics, a good Dj boothe on stage and so, although it's not VERY big (Not tiny, but it couldn't hold 20,000 people kind of scenario), but it's like a little concert everytime you go. So theres a concert atmosphere but also the comfort of a cozy bar and side rooms and everything. I love it. AND, it can be used for ANY music.
For, deep, slushy, underground nights. Mercatcross WAS the best. In the basement there, but I don't know what they've done to it now. Then, Bunker Lounge was great as like, the new dirty underground scene, as in, it was well hidden, but right under everyones nose. It had grafiti and everything and was just really nice, so we started throwing nights there.
We had our last one last Friday, and it was really good, theres video available on facebook and everything. I think youtube as well. Thats why I chose to work there because I could see exactly what it was perfect for. But now that might close also and we are with out a home.
Alot of the big festivals and rave kind events here are held at Telstra Dome, which isn't really a club it's a sporting venue, but the most popular parties with thousands of people and lots of international DJ's are held there, but they're not things I'd go to.