Jetpack by WordPress.com

http://wordpresswave.com/top-plugins-for-wordpress/
http://wordpress.org/plugins/jetpack/
Jetpack is a WordPress plugin that supercharges your self-hosted WordPress site with the awesome cloud power of WordPress.com.You'll also be able to get stats about your site, manage subscriptions, gravatars,recent tweets widget,mobile theme,site monitor for downtime, social networks posting, and more.