The Top 20, which show how broadly a "speech" can defined are:
I'm not familiar with all of these yet I think it would be hard to beat the winner, which can be seen here. It's worth listening to it all.
As a spinoff from the main event, ABC RN's Bush Telegraph is running a poll to find the most inspiring speech of rural Australia. Voting is still in progress, though to vote you have to choose one of nine nominated speeches, which you can see here.