In general, books and journal articles will be the main sources of information for your academic work. However, a number of other reliable sources of information are available. These include:
Conference Papers - academic papers presented at conferences
Working Papers - pre-publication academic research papers
Official Publications - publications by national governments and IGOs
Exam Papers - Searchable collection of past exam papers.
Use the drop-down links under the Other Resources tab for more information.
There are an increasing number of online resources that provide access to primary source material, i.e. original documents. The following may be of interest: