If you haven't yet pushed your changes, you can also do a soft reset:
git reset --soft HEAD^
This will revert the commit, but put the committed changes back into your index. Assuming the branches are relatively up-to-date with regard to each other, git will let you do a checkout into the other branch, whereupon you can simply commit:
git checkout branch
git commit
The disadvantage is that you need to re-enter your commit
