This is what I know about Melbourne scholarships.
National Scholarships are given to all students who score 99.90 and 99.95. You do not have to apply for them.
Victorian scholars receive $15,000 in payments + a HECS exempt degree
Interstate scholars receive $30,000 in payments + a HECS exempt degree
There are also ~10 of these scholarships available to students who have applied for SEAS and scored highly, but not quite high enough to get 99.90+ (I know someone with 99.70 who got one)
Then there are access scholarships. These are based on your SEAS application and ATAR. You don't need a ridiculously high ATAR to receive one of these. ~95 with a decent SEAS application and you will probably get one.
Access scholars receive:
First year $6500, Second year $4000, Third year $3000. You still have to pay HECS.
Then there are faculty specific scholarships which you have to apply for directly to the faculty.
I only know about the Biomedicine one, but I assume there would be others for different faculties.
The Biomedicine Scholarships (I think they give out 5) are worth $18,000. You still have to pay HECS.
Two people who I know got these both scored 99.85.
You can read more about scholarships here:
http://www.services.unimelb.edu.au/scholarships/ugrad/future/index.html