Kathleen M. Ashley's Introduction to the Play
http://www.lib.rochester.edu/camelot/teams/ashint.htm
An excellent detailed scholarly introduction to Mankind, once published in an edition and now made available online. An excellent read for the college student preparing to study the play in detail, it is particularly good on the dates of the text itself.
Middle English Text and Translation of Mankind
http://research.uvu.edu/mcdonald/3610/mankind.html
Excellent translation and side-by-side Middle English text of the play for the college student.