Trailing-whitespace is a project mainly written in Vim Script, it's free.
Highlights trailing whitespace in red and offers:FixWhitespace
This is a mirror of http://www.vim.org/scripts/script.php?script_id=3201
This plugin causes all trailing whitespace to be highlighted in red.
To fix the whitespace errors, just call :FixWhitespace. By default it operates on the entire file. Pass a range (or use V to select some lines) to restrict the portion of the file that gets fixed.
The repo is at http://github.com/bronson/vim-trailing-whitespace
Based on http://vim.wikia.com/wiki/Highlight_unwanted_spaces