I've attached a modified Vim syntax highlighting file for lammps scripts (the current one is located at tools/vim/lammps.vim). I added some more keywords, including the new "elif" from the 19 Nov patch and the "nthreads" keyword from Axel's lammps-icms. It also includes the underscore in variable names between braces (e.g. "${variable_name}").
Since I am not really a vi person, I created an emacs lisp file (attached) to do similar syntax highlighting in emacs. It will be in tools/emacs shortly. Just insert or load it into your emacs init file. If anyone wants to take a stab at improving my attempts to define regexp variables, feel free.