Science Watch in 2002 published rankings of Mathematics Departments from all over the world, based on quantity (total number of citations) and quality (impact made by papers). UNSW School of Mathematics was ranked number 14 on the quality index, and was the only University outside North America and Europe to make this list. UNSW Mathematics is number one in Australia for both quality and quantity.
Update Nov 2007
There have been no official reports on the same topic since 2002. However, an analysis of ISI's Essential Science Indicators data for 1997-2007 confirms the results of 2002. It shows institutional rankings in Mathematics for the decade to 2007, by three criteria: number of papers appearing in ISI journals, number of citations, and citations per paper. Only three Australian institutions are in the list (of 167), and of these ANU and UNSW share the honours: ANU produced slightly more papers, but UNSW had the most citations by total number and the most citations per paper.