To cite MLMES in publications use:

  Sanders, E. A., Konold, T. R., & Cheng, Y. (in press). Model-based
  effect sizes for multilevel linear regression coefficients.
  Methodology: European Journal of Research Methods for the Behavioral
  and Social Sciences.

A BibTeX entry for LaTeX users is

  @Article{,
    title = {Model-based effect sizes for multilevel linear regression coefficients},
    author = {Elizabeth A. Sanders and Timothy R. Konold and Yijun Cheng},
    journal = {Methodology: European Journal of Research Methods for the Behavioral and Social Sciences},
    year = {in press},
  }