Redback Spider

Yep, that's right. Here's a good shot of the red on their back: http://www.projectnoah.org/spottings/5920268

That's right, the Black Widow just has the hourglass underneath the abdomen...right?

ceherzog, the Redback is very closely related to the Black widow. Redbacks are red on the back as well as the underside, hence the name.

Do they have Black Widow's in Australia? That's what it look like to me.