For attending conference,
*. an application form for business trip, can be downloaded from the embassy website;
*. the invitation;
*. a bank statement (cost s$15 in DBS), transaction records;
*. an official letter to certify your purpose in Austrilia; (maybe not necessary, but I was requested to produce such a letter from my department last year);
*. S$70

maybe airticket and hotel booking record needed.
The visa can only be granted one month before your trip, do not go there too early.