IG-88B (Star Wars)
Porygon (Pokemon)
SHODAN (System Shock)
T-1000 (Terminator 2: Judgement Day)
Yuki Nagato (The Melancholy/Dissapearance of Haruhi Suzumiya)
--
HK-47: The very best there is when you absolutely positively have to kill every meatbag in the room. Accept no substitutes!