To cite sandwich in publications use:

Achim Zeileis (2004). Econometric Computing with HC and HAC Covariance Matrix Estimators. Journal of Statistical Software 11(10), 1-17. URL http://www.jstatsoft.org/v11/i10/.

If sandwich is applied to models other than lm() also cite:

Achim Zeileis (2006). Object-oriented Computation of Sandwich Estimators. Journal of Statistical Software 16(9), 1-16. URL http://www.jstatsoft.org/v16/i09/.

Corresponding BibTeX entries:

  @Article{,
    title = {Econometric Computing with HC and HAC Covariance Matrix
      Estimators},
    author = {Achim Zeileis},
    journal = {Journal of Statistical Software},
    year = {2004},
    volume = {11},
    number = {10},
    pages = {1--17},
    url = {http://www.jstatsoft.org/v11/i10/},
  }

  @Article{,
    title = {Object-oriented Computation of Sandwich Estimators},
    author = {Achim Zeileis},
    journal = {Journal of Statistical Software},
    year = {2006},
    volume = {16},
    number = {9},
    pages = {1--16},
    url = {http://www.jstatsoft.org/v16/i09/.},
  }