To move the branch pointer of a checked out branch, one can use the
git reset --hard
N.B. If you simply want to move a branch to another commit, this method is probably not the easiest option.
branch -f as detailed by Chris Johnsen is a simpler command, so see his answer.
You can do it for arbitrary refs. This is how to move a branch pointer:
git update-ref -m "reset: Reset <branch> to <new commit>" refs/heads/<branch> <commit>
The general form:
git update-ref -m "reset: Reset <branch> to <new commit>" <ref> <commit>
You can pick nits about the reflog message if you like - I believe the
branch -f one is different from the
reset --hard one, and this isn't exactly either of them.