Here's another one by Jon Cave at Lions Go Roar, which allows you to define two email addresses which will receive notifications:

http://lionsgoroar.co.uk/wordpress-plugins/update-notifier/

Repository page:

http://wordpress.org/extend/plugins/update-notifier/

I have no idea if Jon's plugin takes the approach suggested by Donncha, of checking wp_version_check(), or if Konrad Karpieszuk's plugin can also accept two email addresses.