Using Underscore Templates in WordPress

Your plugin index file:

add_action( 'print_media_templates', 'wpse8170_admin_footer' );
function wpse8170_admin_footer() {

    require 'templates.php';
}

Your templates.php:

<script id="tmpl-mytemplate" type="text/html">
    <h1>Hello {{data.name}}!</h1>
</script>

Your media js file:

wp.media.view.MyView = wp.media.View.extend({
    template: wp.media.template('mytemplate'),

    render: function() {
        this.$el.html(this.template({name: 'world'}));
    }
});