One of the most useful plugins I have is an automatic updater.  This thing is great because all you do is click one button and it goes out to Wordpress.org and downloads the most up to date file unzips it and installs it.  Before it does that it creates a backup of your files and disables plugins.  After install it restarts all your plugins and makes upgrading as easy as clicking one button.  This is great because it saves me time of downloading the new file unzipping and uploading via FTP.  Just click the Wordpress logo to get the plugin.