Admin Tools is a definitably no-brainer to use on any Joomla! website. It can notify you about and install new Joomla! releases, fix your files' and directories' permissions, protect your administrator directory with a password, change your database prefix, set a secure Super Administrator ID, migrate links pointing to your old domain on-the-fly and perform database maintenance, all with a single click. There is a standard core version and also a paid pro version. I find the paid pro version worth the money.
Admin Tools on JED