**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.