A few years ago, I came across a very interesting project by Joseph Scott, called PressFS; it exposed WordPress posts as plain text files on your filesystem. This allowed you to use all your favorite command-line tools to manipulate these posts, including editing their content in your favorite text editor.
With WP-CLI 0.9.0-beta, you can do the same thing:
wp post edit 123
Once you run that command, your $EDITOR will open up, pre-filled with the content of the post with ID 123. After you’ve made your changes and quit the editor, WP-CLI will update the post in the database.
Credit goes to goldenapples for implementing it.