This script creates predefined black and white variations and saves them as layers. Users can choose which variations should be created.
For more sophisticated possibilities use the channel mixer or other tools. This script just uses typical black and white variations, to provide a quick overview - just switch the layers visibility afterwards.
Install to .gimp-2.6/scripts in your homedir as bwvariations.scm, then start GIMP or click Script-Fu->Script refresh, you'll find it then under Script-Fu->Misc->bwvariations