While I cannot post it here for obvious reasons, my favorite movie ending would probably have to be the finale of Nagisa Oshima's In the Realm of the Senses (1976), where Sada strangles her lover Kichi to death during sex (with his permission), then cuts off his genitals and writes "SADA + KICHI TOGETHER FOREVER" in blood on his chest before wearing his severed genitals as a necklace. It really doesn't get much more memorable than that (especially since this film was very much based on a true story).