~/.js
dotjs is a Google Chrome extension that executes JavaScript files in ~/.js based on their filename.
If you navigate to http://www.google.com/, dotjs will execute ~/.js/google.com.js.
This makes it super easy to spruce up your favorite pages using JavaScript.
See https://github.com/defunkt/dotjs for full installation instructions. You need to run a server in addition to this Chrome extension.
Only works on OS X.