As of WordPress 3.4.2, the Editor sub-menu under Appearance will give you access to your theme files. I forget it’s there, usually. Today I realized I had reason to want to lock it up.

Why?
Security. Your editor is a gateway for hackers and other unkind folk. Lock that thing up.

How?
So easy. So, so easy. Add this to your functions.php:

function remove_editor_menu() {
  remove_action('admin_menu', '_add_themes_utility_last', 101);
}
add_action('_admin_menu', 'remove_editor_menu', 1);

Done.

Wwwowie zowie. Be happy.