comment-pln – Comment macros for use in Plain TeX
Defines macros \comment and \endcomment such that everything between the two is ignored.
Maybe you are interested in the following packages as well.
- multiaudience: Several versions of output from the same source
- xcomment: Allows selected environments to be included/excluded
- xifthen: Extended conditional commands
- draftfigure: Replace figures with a white box and additional features