Commentary can be a hard concept to understand without examples to guide you. Beside the wonderful examples and explanations presented in Richard Straub's and Summer Smith's articles, I have included links to some of my own commentary and the papers on which those comments were based.

Examples from Straub's article
Straub's example of Directive commentary
White's Commentary
Peterson's Commentary
Gere's Commentary

Smith's Article

My first commentary: Complete with evaluation from my professor and trainer Dr. Essid, this commentary is a good example of directive commentary.
My two page commentary: This commentary tackles an "offensive" paper that needed a lot of revision.
My English as a Second Language commentary: This commentary is a combination of directive and facilitative commentary because of the unique ESL field. For more background on ESL take a look at a project complied by my classmate John Lee.