WHAT IS THE LITERATURE?

Although you might think of novels and poetry when you hear the word "literature," for a piece of research the meaning is more specific. In terms of a literature review, "the literature" means the works you consulted in order to understand and investigate your research problem.

Journal articles: these are good especially for up-to-date information. Bear in mind, though, that it can take up to two years to publish articles. They are frequently used in literature reviews because they offer a relatively concise, up-to-date format for research, and because all reputable journals are refereed (i.e. editors publish only the most relevant and reliable research). Books:  books tend to be less up-to-date as it takes longer for a book to be published than for a journal article. Text books are unlikely to be useful for including in your literature review as they are intended for teaching, not for research, but they do offer a good starting point from which to find more detailed sources.
Conference proceedings: these can be useful in providing the latest research, or research that has not been published. They are also helpful in providing information on which people are currently involved in which research areas, and so can be helpful in tracking down other work by the same researchers. Government/corporate reports: many government departments and corporations commission or carry out research. Their published findings can provide a useful source of information, depending on your field of study. Newspapers: since newspapers are generally intended for a general (not specialized) audience, the information they provide will be of very limited use for your literature review. Often newspapers are more helpful as providers of information about recent trends, discoveries or changes, e.g. announcing changes in government policy, but you should then search for more detailed information in other sources. Theses and dissertations: these can be useful sources of information. However there are disadvantages: 1) they can be difficult to obtain since they are not published, but are generally only available from the library shelf or through interlibrary loan; 2) the student who carried out the research may not be an experienced researcher and therefore you might have to treat their findings with more caution than published research.
Internet: the fastest-growing source of information is on the Internet. It is impossible to characterize the information available but here are some hints about using electronic sources: 1) bear in mind that anyone can post information on the Internet so the quality may not be reliable, 2) the information you find may be intended for a general audience and so not be suitable for inclusion in your literature review (information for a general audience is usually less detailed) and 3) more and more refereed electronic journals (e-journals) are appearing on the Internet - if they are refereed it means that there is an editorial board that evaluates the work before publishing it in their e-journal, so the quality should be more reliable (depending on the reputation of the journal). CD-ROMS: at the moment, few CR-ROMs provide the kind of specialized, detailed information about academic research that you need for your own research since most are intended for a general audience.  However, more and more bibliographies are being put onto CD-ROM for use in academic libraries, so they can be a very valuable tool in searching for the information you need.
Magazines: magazines intended for a general audience (e.g. Time) are unlikely to be useful in providing the sort of information you need. Specialized magazines may be more useful (for example business magazines for management students) but usually magazines are not useful for your research except as a starting point by providing news or general information about new discoveries, policies, etc. that you can further research in more specialized sources.