In the early 2000s, CELT created a useful tutorial "Guide to Referencing". The Library now houses it on its web server. It has some interactive elements using flash.
Duke University Libraries: Citing Sources - website
Provides examples of references in popular citation styles.
Harvard system of referencing - website
Anglia Ruskin University
The Purdue Online Writing Lab (OWL) - website
Contains over 200 links related to writing research papers, business letters, citation styles and many others.