The Quick Logout component adds a new menu item type to Joomla 2.5 and 3.x that logs a registered user out without the confirmation step. In addition, you can specify the page to redirect the user to when logging out. When Joomla is configured to use a "guest" user group, you can set this menu item to show to "registered" users, and combine it with a "Login" menu item that is set to show only go "Guest" users. If these 2 menu items are next to each other on the menu, it appears to be a single menu item that switches from "Login" to "Logout" depending on the status of the user.