There is a certain hype about mixed (and random) effects among statistician and analysts. You can show some love to Douglas Bates and Martin Maechler for maintaing the lme4 package for our cupid, R
I copy the entity of the information of the projects page.
Doxygen documentation of the underlying C functions is here.
The project summary page you can find here.
References to articles and other research using nlme or lme4 can be found here. The LaTeX bibliography file can be accessed from here. If you would like to add your work to this database, please email vasishth.shravan at gmail dot com
Slides from short courses on lme4 are here.
Chapter drafts of the book lme4: Mixed-effects Modeling with R are available here.
To complete this quick post, I append the following vignettes.