The current Australian flag isn’t that great. I really like the design of the flag of the Australian Capital Territory:
The basic structure could be used for a national flag, with something other than the ACT coat of arms on the right. This design would work best if our national colours were blue and gold. I wish they were, but at the moment we’re stuck with the relatively awful green and gold (although blue and gold apparently are the heraldic colours of Australia). So, I propose that the national colours of Australia be changed when we bring in the new flag (and system of government?).