Before buying certificates, check whether there is a free alternative!
The sources mentioned below are in Queensland, but similar records exist in many interstate and overseas repositories.
Before buying a certificate from the Queensland Registry of Births Deaths and Marriages, check whether that certificate is included in a file at Queensland State Archives. If it is, you can either take a digital photograph or save an image to a USB memory stick free of charge. (The Archives keep changing their Web site, so use Google to find the current URL.)
At the Archives you can often see certificates that you cannot buy from the Registry (because of differences in access restrictions). Certificates in archival files are often
more accurate than typed copies issued by the Registry now.
From about the mid-1890s onwards, most Queensland Supreme Court 'will' files, and some 'intestacy' files, contain the death certificate. There are also probate files in Queensland for many people who died in other States and countries.
I sometimes find that the information on the death certificate in a probate file and the information on the certificate you bought from the Registry are significantly different! In one case the certificate in the probate file listed children who were not mentioned on the copy my client had bought from the Registry. In another case the probate file's copy showed that a person had lived in both the Northern Territory and Queensland (and how long in each place), but a more recent typed certificate from the Registry did not mention that.
I have seen birth, death and marriage certificates (including some from overseas) in many series of records. They include (but are not limited to):
More information about those sources is in the book
Tips for Queensland Research. For wills and probate records see also
Queensland Genealogy and Archives Research Tips.
Postscript 1: For the rest of Australia, see
Kerry Farmer's suggestions re certificates.
Postscript 2: A friend and I are creating an index for certificates that we find in odd places in Archives files. In the future, names from that index will be added to
my main Web site.