Edit ICO, PNG, and GIF icons. No really. They're converted with ImageMagick to XPM, a plain text image format with beautiful syntax highlighting in GUI versions of Vim. Here, it's easier just to show you:
And yes, I did say edit. Obviously you're not going to be uninstalling Photoshop anytime soon, but for stupid simple tweaks, it gets the job done.
Oh, and it can also handle PDFs (with pdftk), Word Documents (read-only, with Antiword), and Mac OS X plist files.
If you don't have a preferred installation method, I recommend installing pathogen.vim, and then simply copy and paste:
cd ~/.vim/bundle
git clone git://github.com/tpope/vim-afterimage.git
Once help tags have been generated, you can view the manual with
:help afterimage.
See the contribution guidelines for pathogen.vim.
Like afterimage.vim? Follow the repository on GitHub and vote for it on vim.org. And if you're feeling especially charitable, follow tpope on Twitter and GitHub.
Copyright (c) Tim Pope. Distributed under the same terms as Vim itself.
See :help license.