Purdue University Online Writing Lab (OWL) - an extensive guide to research, writing, and formulating citations.

Both Citation Machine  and BibMe are free and easy to use. They create a citation for you automatically. 

Printable PDF - Handout - How to Cite: MLA (PDF document, from the University of Iowa Libraries)

Examples

Mergent database:

PepsiCo Inc. 2000 Annual Report. Purchase, NY: PepsiCo Inc., 2000. Mergent Online.   
     Frederick S. Pardee Management Library, Boston, MA. 22 Nov. 2004.   
      http://www.mergentonline.com/compsearch.asp

See more examples at Citing Business Sources by Boston University Libraries