One of the nice workflows that's already built in to the git command line tools is this one. When you're working on a branch and realise that a commit you made a few commits back has a mistake in it:

    # Make correcting change
    git commit --all --fixup=<ref of commit with mistake>
    # Continue working on branch, then at some point
    git rebase --interactive --autosquash

The --fixup option creates commits with subjects formatted like 'fixup! previous commit subject'. --autosquash uses these subjects when building the interactive rebase list.

Handy enough that I set rebase.autoSquash to true in my ~/.gitconfig so 'git rebase -i' always works like this.