Australian languages are usually classified into two main groups. The first group is a large family spanning the continent, Pama-Nyungan. The other group is not a family but merely an "everything else" category, Non-Pama-Nyungan.
Of the languages that still have a large number of speakers (in the thousands), all the ones I can think of are I believe Pama-Nyungan: Arrernte, Kala Lagaw Ya, Pitjantjatjara, Warlpiri.
This makes me wonder which language is the most spoken but not a Pama Nyungan language?