Israel has the most effective method by far; it's called the Mossad. Especially in the Middle East, the Mossad has successfully infiltrated every significant military organization. Israel knows what's going to happen weeks before it actually does (and sometimes, they can even make it happen.)
Australia?
First of all, Bush and Blair look quite the fools, standing alone against the unseen forces of Evil. Getting another country to cooperate would have made things look a lot better. The problem with Australia was that the public was almost universally opposed to Bush's War on Terror. Finally, after much arm twisting, their government half-heartedly threw in their support. It was shortly after this that the bombing occurred. Now... you can go either way with this. The true believers will maintain that the Muslim extremists decided to lash out immediately at the War On Terror's newest ally. The conspiracy crowd says that the explosion was used to prove to the doubtful Australian population that the International Terror Network actually does exist and is targeting all member of "The Alliance."
Once again, we have a huge explosion for which no one takes credit for. Add it to the growing list: 9-11, OKC bombing, The Cole, The London "Mega-Bombs..." Generally, terrorists can't wait to take credit for attacks against their enemies. I mean, back in the good-old-days, you couldn't find the culprit because everyone would take credit for the attack.
I'm still reading about the Bali blast.