Great aboriginal leaders or great leaders since the first fleet?
This question is a little vague and broad, so if you have any areas you're specifically interested in, perhaps list those... So I'll just list some leaders I really like...
Classic lefty Prime Minster from the 70s, led a radical and divisive government, and was eventually removed by the Governor General in what is the biggest scandal ever in Australian politics... The Dismissal is still talked about today.
As Prime Minister, he started the process of withdrawal from Viet Nam, made higher education free, had his Attorney General raid the domestic spy agency (with the AG himself knocked in the door with a sledgehammer), abolished the death penalty, and started legal aid...
http://en.wikipedia.org/wiki/Gough_Whitlam
Also has a famous rock band named after him: http://www.youtube.com/watch?v=15eH6roFWgU
An Engineer and General in WWI. Despite being Jewish, rose to the top of the Australian army during WWI. He also led many of the first successful combined attacks with tanks and infantry, which hadn't been used well in the middle parts of the war. After the war, he also restored order and stopped the rioting in Melbourne during the police strike, by using a few thousand veterans as a make-shift force.
http://adb.anu.edu.au/biography/monash-sir-john-7618
http://en.wikipedia.org/wiki/John_Monash
Among Aboriginal leaders, the two most famous are probably Vincent Lingiari and Pemulwuy...
He was fought a long are somewhat effective campaign against the first settlers, and his son took up the fight after he was killed.
http://en.wikipedia.org/wiki/Pemulwuy
He was an Elder and a stockman on the Vestey estates in the NT, who led a campaign to get traditional land rights recognised. Lingiari led what was basically a strike, against conditions, and the lack of ownership of what was once their traditional lands. It was the start of a long land rights battle in Australia...
http://en.wikipedia.org/wiki/Vincent_Lingiari
This song is written about him, by Paul Kelly (our most famous folk singer) and Kev Carmody, who worked on the Vestey estates, you'll also notice Whitlam is mentioned in the song: http://www.youtube.com/watch?v=6_ndC07C2qw
We lost him... While he was prime minster... Never found...