If you are using Forms Authentication it should suffice to create your own button which calls FormsAuthentication.SignOut(); and then redirects the user to a new page.
You can also use the System.Web.UI.WebControls.LoginStatus control. You can see an example of this in the EPiServer public templates demo site.
Thanks for the help!
I found the easiest way to logout from form authentication is to just us a link that points to the logout page that resets the cookie.
A logout possibility as a button or link to add to pages that requires authentication to read.
In CMS 5 it is only possible to logout from the edit or admin mode, this causes a problem when you have a Intranet that is accessibly over the Internet trough login (only authenticated users can read the page). Today the only way to logout if do not have access to edit mode is to close the browser. It works but is not user friendly and reduces the security of the system.