This resource, part of Diana Hacker's Research and Documentation Online site, answers most questions. Discusses print and online source citation formats.
MLA Handbook for Writers of Research Papers. (7th ed.) Modern Language Association of America, 2009.
This is the ultimate source on MLA Style. Chapter 5 deals with preparing the list of works.
Hacker's excellent guide for student writing is recommended by W&L's Writing Program Advisory Committee.
Hacker, Diana. Research and Documentation in the Electronic Age. (5th ed.) Bedford/St. Martin's, 2010.