To cite lavaan in publications use:

Yves Rosseel (2012). lavaan: An R Package for Structural Equation Modeling. Journal of Statistical Software, 48(2), 1-36. URL http://www.jstatsoft.org/v48/i02/.

Corresponding BibTeX entry:

  @Article{,
    title = {{lavaan}: An {R} Package for Structural Equation
      Modeling},
    author = {Yves Rosseel},
    journal = {Journal of Statistical Software},
    year = {2012},
    volume = {48},
    number = {2},
    pages = {1--36},
    url = {http://www.jstatsoft.org/v48/i02/},
  }