Influence.ME is an R package that helps detecting influential cases in multilevel regression models. It has been around for a while now, and recent changes in lme4 broke the functionality of using influence.ME with sampling weights.
Thanks to a kind contribution of some code by user Jennifer Bufford, influence.ME now should work with multilevel models with sampling weights (and offsets). Version 0.9-5 is now available on CRAN servers around the world.
For more details on influence.ME, see: http://www.rensenieuwenhuis.nl/r-project/influenceme/