Law & Order CanceledThey say that all good things must come to an end, but some endings are still more surprising than others. Case in point: 'Law & Order,' which has been canceled by NBC after a groundbreaking 20-year run that established it as not only one of the longest-running shows in television history, but one of the most influential.

But it's not only 'Law & Order's' longevity that sets it apart; it's also the cast. While most hit television series rely on one or two stars to carry the franchise, over the last two decades 'Law & Order ' has survived -- and thrived -- on massive, constant cast turnover, with more than thirty actors getting face time during the show's iconic opening credits.