For some webdesign projects, you may need to prevent admin access for logged in users. To do so, simply paste following snippet to your functions.php file:

function prevent_admin_access()
    if ( false !== strpos( strtolower( $_SERVER['REQUEST_URI'] ), '/wp-admin' ) && !current_user_can( 'administrator' ) )
        wp_redirect( home_url() );
add_action( 'init', 'prevent_admin_access', 0 );

This code will prevent any users to access administration panel. Administrators however will still be able to access the panel.