Often professors will ask you to find information from credible sources. This is to ensure the information you find is valid, valuable, and related to your profession. Further, you should begin reading trade journals–the publications specializing in your field– so you are aware of the current trends and changes in the field.
Students generally know that Wikipedia is not a credible source and that academic papers are, but what are trade journals? What about Time or BusinessWeek. What other sources are credible?
Follow this link for a chart that details types of publications and gives examples:
http://gethelp.library.upenn.edu/PORT/infotypes/scholarly_popular.html