For a guy who's normally as far from the action as one can get, credit has to be given to Obadiah Stane in the second half of the season 2 pilot. Kidnapped by Whiplash and imprisoned, he fakes being sick to a guard so he'll be let out. Then he punches the guard and takes his gun, pistol-whipping the guy unconscious. If it weren't for Blizzard, Stane may have actually made his way out.
Nearly everything that Whitney Stane does as Madame Masque is made of awesome.
Pepper taking over Tony's armor when he's knocked out in "The Might of Doom", then blasting Dr. Doom into a building so hard it collapses. Someone get that girl some armor!
One step closer in "Hostile Takeover". Remote-controlling the empty stealth armor to save Tony and kick some ass on the side. Tony's so impressed that he agrees to make a suit for her.
There's just something awesome about Happy being the one to solve one of the Mad Thinker's questions that no one else could get. Especially since she spent so a lot of time this season going out of her way to call him an idiot.
Mr. Fix gets one when he engineers an epicVillainous Breakdown for Justin Hammer, getting him to systematically eliminate all the criminals he hired for protection, aiding Iron Man in exposing him as a criminal, then dousing him with his own zombie gas after Iron Man beats him as Titanium Man. That last bit may have been going overboard, but given all the crap that Justin put Fix through, you can't really blame him for going the extra mile.
Tony's epic rematch with Agent Mallen. After getting Curb Stomped by Mallen in his first encounter, Tony turns the tables by taking a dose of extremis. Even Nick Fury admits it, referencing a certain team he is building...
At the end of "Designed Only for Chaos" the Living Laser coming to Tony's rescue after he realizes that Tony has only ever tried to help him.
Magneto as well, who spends most of his episode throwing Iron Man and War Machine around like ragdolls and showing just what a master of magnetism is capable of. The show actually had to add in a new weakness (he can only control positive or negative fields, not both at once) just to give them a fighting chance.