Nope, no visas required for tourists from the USA, I think for up to three months.
I haven't looked at it myself for ages and I probably said something I'd be embarrassed about now, but maybe check out the little journal I put up about my first visit to Australia in 1999. Should still be there at
www.gingerroot.com/oztrip.
There's more tourism in remote Aboriginal land all the time. The most established business around here is Bawaka tours. Bawaka's definitely up there on the list of most gorgeous places in the world. They'll even take you to visit Yirrkala Arts before or after.
A little article with some info...