4. FarSight XR-20
The FarSight defined hacks-to-the-max back in the Perfect Dark days, when online multiplayer (and the real hacks that came along with it) were only sparkles in young console gamers' eyes.
It was the ultimate tool in multiplayer. Not only did it use magic alien thermal sensors to pinpoint opponents' locations, but it also let you simply shoot through any walls in between and take them out in one hit. We'd have entire games of hide-and-seek where one player would have the FarSight and the other four would simply run around in circles and see how long they could last.