Did quite a bit of riding out there last year over a period of 5 months and rode in several states, (geographical ones mostly!). I found this site was a great way of figuring out places to go in each region and then having a look on youtube to see what the trails were actually like.
http://www.trailmate.com.au/
Couple of observations. It’s a very big and often very remote place to ride, there were plenty of times where I’d driven for 1-2 hours out of civilisation to get to some trails, then ridden 1-2 hours away from the car and didn’t see another person all day. Made me ride a bit more carefully and take it a bit easier on some of the descents! Other than that, dry, warm, dusty, lots of great trails, got to explore some incredible places I would never have otherwise seen, loads of wildlife etc. (Flying down a narrow descent to find a huge red kangaroo sunbathing in the middle of the track with nowhere to go is not quite the same as startling a rabbit back in the UK!)