WordPress Tags-Like Meta Box
The WordPress tags meta box has a great interface for dealing with data. This helper class will allow you to customize a tags-like meta box of your own with ease.
Include the class file anywhere (in your plugin or theme), and then instantiate the class.
$myVersionOfTags = new Tags_Like_Meta_box( array( 'ID' => 'post-notes', 'nice_name' => 'Notes' );
By default the meta box is added over all post types, and saves any data into a piece of post meta for the post.
If you want to edit the capabilities, just create a subclass and edit away!