13. Battlestar Galactica - Season 1 Finale (Kobol's Last Gleaming Part 2)
Battlestar Galactica wasn't afraid to leave viewers hanging. Throughout the course of season one Boomer had begun to suspect the worst; that she was a Cylon. By the season finale you knew it for certain, but she still wasn't sure. At least not until she encountered another version of herself on the Cylon base star orbiting Kobol. But even then viewers hoped she would fight her programming and fight for humanity. That hope was dashed in the final stunning moments of season one as Boomer's programming was activated and she pulled out her gun, shooting Admiral Adama several times in the chest. As Adam lay bleeding on the table and all hell broke loose, audiences were left shocked and desperate for the second season. Fortunately it wouldn't disappoint, though the ramifications of this cliffhanger would last long into season two.