The fortran namelist syntax is defined in a few places, like on the Intel website and at http://owen.sj.ca.us/~rk/howto/slides/f90model/slides/namelist.html. I'm not sure if these are complete or even consistent, but some syntax highlighting would be better than none. Is there any such syntax highlighter?
Adding this to ~/.vimrc
allowed vim to recognise namelist files as fortran files, and the syntax highlighting that is applied is adequate:
if has("autocmd")
au BufNewFile,BufRead *.nml set filetype=fortran
au BufNewFile,BufRead *.namelist set filetype=fortran
endif