SET DATEFORMAT DMY

 SELECT SomeStringDate
,       ConvertedToDateTime = CAST(d.SomeStringDate AS DATETIME)
   FROM (
         SELECT '15-03-05'      UNION ALL
         SELECT '15/03/08'      UNION ALL
         SELECT '15/03/2005'    UNION ALL
         SELECT '15.03.2005'    UNION ALL
         SELECT 'March 15 2005' UNION ALL
         SELECT 'Mar 15 2005'   UNION ALL
         SELECT '15 March 2005' UNION ALL
         SELECT '15 Mar 2005'   UNION ALL
         SELECT '20050315'
        ) d (SomeStringDate)
;