To cite relaimpo in publications use:

Grömping U (2006). “Relative Importance for Linear Regression in R: The Package relaimpo.” Journal of Statistical Software, 17(1), 1–27.

Your version of package relaimpo: R package version 2.2-5

Corresponding BibTeX entry:

  @Article{,
    title = {Relative Importance for Linear Regression in R: The
      Package relaimpo},
    author = {Ulrike Grömping},
    journal = {Journal of Statistical Software},
    year = {2006},
    volume = {17},
    number = {1},
    pages = {1--27},
  }