If you have been to any of the countries listed below within the last six days before arriving in Australia, you'll have to show a valid immunization certificate for yellow fever.
You need that immunization certificate for yellow fever arriving from:
Angola · Equat.Guinea · Ethiopia · Benin · Bolivia · Brasil · Burkina Faso · Burundi · Ecuador · Ivory Coast · French Guyana · Gabun · Gambia · Ghana · Guinea · Guinea-Bissau · Guyana · Kamerun · Kenia · Columbia · Rep. of Kongo · Liberia · Mali · Niger · Nigeria · Panama · Peru · Rwanda · SaoTomé & Principe · Senegal · Sierra Leone · Somalia · Sudan · Suriname · Tanzania · Togo · Tschad · Uganda · Venezuela · Kongo, Democrat. Rep. · Sambia · Centr. Afr. Republic
Generally it is recommended to be vaccinated against tetanus and diphtery.
In addition you should consider to become vaccinated against Hepatitis A and Hepatitis B. The first depends on your way of travelling and your inhabitation conditions. The second will be fine if your stay is very long or you have tight contact to natives.
Further information (German): www.travelmed.de.