How to undo a git commit --amend

I made a silly mistake this morning, accidentally doing a git commit amend instead of a new commit. Here's how to roll back:

http://www.youtube.com/watch?v=pW0bITv07ok&feature=youtu.be

Thanks to http://stackoverflow.com/questions/1459150/how-to-undo-git-commit-amend-done-instead-of-git-commit

And the git documentation!