Blimply allows you to send push notifications to your mobile users utilizing Urban Airship API. It sports a post meta box and a dashboard widgets. You have the ability to broadcast pushes, and to push to specific Urban Airship tags as well.
You will need an Urban Airship account in order to be able to use this plugin. The plugin features the ability to send push notifications for posts/pages/custom post types, and a handy Dashboard widget.