Kinetron and Caliber, from 4th Edition High Tech Enemies and 4th Edition Dark Champions respectively. Kinetron is an absolute monster when charged up, capable of tossing around your typical hero team. Where Kinetron is smart hammer, Caliber is a scapel wielded by a maniac. You got a tough hero with a weakness to certain attack? Caliber can tailor himself to deal with it. Need to lay down cover fire for the Viper agents to get away and not reveal your position? Caliber's got it handled. Need a nutjob willing to go out the front of the bank and shoot it out with the cops? Caliber. Or his future replacement, which of course Viper will equip after the latest one gets himself killed.
Honorable mentions to Boomerang and Starhand from 4E Challenges for Champions, and Buzzsaw and Wallbanger from 4E Champions Presents #2. All four are great simple mooks. Wallbanger has the same gimmick as Kinetron which makes him pretty dangerous despite being only middling power wise, Boomerang is your typical blaster, Starhand is a brick with a couple of neat tricks and Buzzsaw your close combat specialist.