To cite plm in publications use:

Yves Croissant, Giovanni Millo (2008). Panel Data Econometrics in R: The plm Package. Journal of Statistical Software 27(2). URL http://www.jstatsoft.org/v27/i02/.

Corresponding BibTeX entry:

  @Article{,
    title = {Panel Data Econometrics in {R}: The {plm} Package},
    author = {Yves Croissant and Giovanni Millo},
    journal = {Journal of Statistical Software},
    year = {2008},
    volume = {27},
    number = {2},
    url = {http://www.jstatsoft.org/v27/i02/},
  }