In the climax of the Level Upper arc, Mikoto battles a creature formed from the AIM Dispersion fields of ten thousand individuals, which Kiyama dubs "AIM Burst". After the AIM Burst loses its Healing Factor, she proceeds to cut loose and use her full power, releasing a blast of electricity so intense that, even though the creature blocks it with a barrier, the heat generated from all of the electricity is still more than enough to completely burn its skin off and roast it alive. Then she uses magnetized iron sand to block whatever attacks it throws at her, ripping multiple limbs apart in the process, then finishes it off with her Railgun.
In Episode 24 of Season 1, Mikoto takes down a Humongous Mecha piloted by Telestina by latching onto its Rocket Punch, ripping the projectile to pieces, and then with Kuroko's help, using a large chunk of debris as ammo for a huge Railgun.
Chapter 36: Touma landing the mother of all punches to Accelerator after the latter has been driving Misaka to despair through the Level 6 Shift experiments and boasting of his near-infinite power. In the fight between him and Touma, Accelerator goes a final double-handed strike... and is laid out on his backside in the gravel. Cue freak-out, and a desperate attack, followed bythis.
Saten gets her moment near the end of Episode 24 when she saves Mikoto and the others by smashing Telestina's Capacity Down machine with a baseball bat.
Misaka's entire fight against ITEM on August 19th, but special bonus points for outsmarting the Meltdowner by using her bomb happy companion's own traps against her twice when the constant battles had worn her down.
During the first Railgun SS, Mikoto takes Flight using her power and all but destroys the magicians' ships to protect Liberal Arts City before the lifeboats could escape.
Chapter 51: In the Sports Festival arc in the manga, one of the Sisters gets kidnapped, and Mikoto is forced to stay behind while her friends do all the work, since mind-controlled minions are keeping a close eye on her, and she's not willing to kill them to escape. Until one of said friends gets hurt. She just walks right past, in a straight line towards her goal.
Mikoto: "Unless you are prepared to kill me to stop me, get out of my way."
Chapters 51 & 52: Wannai and Awatsuki completely out maneuvering Baba and his robots leading to his complete defeat.
Chapter 54: In the face of a girl who is threatening her, Kuroko (who is in a wheelchair) teleports out of the wheelchair, over the girl, and throws the damned thing at her!
Episode 1 of Railgun S:
Mikoto stops a helicopter from taking off by pinning it down with magnetism.
Saten catches Erii when the thugs throw her out of the helicopter, nearly dislocating her arm in the process.
Kuroko teleports Mikoto several times in a row so she can catch up to the helicopter. Mikoto destroys it with her railgun upside down while falling from the sky. Kuroko teleports all the thugs to the ground.
Episode 2 of Railgun S: We find out that Shinobu is the one placing cash cards in alleyways and is eventually confronted by a gang of Skill Out thugs who are trying to rob her. With only a dramatic performance, two vials of local anesthesia and some improvised props, she bluffs them into thinking that she has a deadly esper ability that allows her to kill anyone she has ever touched with a thought, and frightens them into leaving her alone.
Mikoto's exploits in Episode 23 of Railgun S are impressive. She got injected with something that shut off her voluntary nervous system, so she proceeds to use her electrical powers to emulate nerve signals, then goes to meet up with her friends who are raiding the warehouse she's held in because she implanted herself with a Tracking Device in case she got captured.
Most of the finale for Railgun S: First with many Judgment members coming to help take down the armored suits, and using Kuroko's Catch Phrase, Mugino and the rest of ITEM lend a hand, Misaka does a vanguard charge to stop the Big Bad from shooting himself, then Saten and Uiharu pilot a Humongous Mecha made by Kongou Airlines, Mitsuko launches said Humongous Mecha into space with her wind powers, and finally Misaka uses said Humongous Mecha as ammo for a huge Railgun to take down a missile IN SPACE.
Kuroko in particular deserves a special mention. During the Silent Party attack, pretty much all of Judgment is focused on just drawing the powered suits' attention and keeping the 20,000 strong army contained. Cue Kuroko teleporting around like a madwoman, one shotting dozens of powered suits at a time with friggin' javelins. After all, they're a threat to onee-sama, and robots are acceptable targets!
Saten takes on the powered-suits with her baseball bat, until everyone's favorite Anti-Skill officer Yomikawa shows up with an even bigger powered suit, which Saten had spent the night before learning to pilot. She then proceeds to kick much robot butt.
ITEM shows up, with Mugino furious that STUDY had sent them around on a number of pointless errands to analyze their abilities, AND copied her powers for their latest robots.
Mikoto stopped the bullet from Arotomi Haruki's gun, but took some damage from it. What does she do? Slaps Arotomi with her wounded hand, leaving her blood on his face. She never once mentions the obvious pain she must be in.
Chapter 63 of the manga sums up why it's awesome on the very last page: "The unprecedented combo of Touma and number seven act to stop Mikoto's rampage!!"
To put it into perspective, this is the first time the two of them ever meet. At first, Gunha dismisses Touma as another normal until the both of them No Sell Mikoto's beams mid-conversation, which then leads the two of them to team up. The fact they are very similar means Touma befriended another Level 5.
To get around Touma's Imagine Breaker, Angel!Mikoto starts flinging massive piles of scrap metal in all directions. And just before she can connect a large ball of it towards him, Gunha does a Big Damn Heroes and obliterates the scrap ball.
In Chapter 68, Kuroko blocks a knife... by letting it embed into her palm. She doesn't even show a twinge of pain and then proceeds to curb stomp Mitori.
Also from Chapter 68, Misaki tricking Gensei into entering Exterior's self-destruct code by switching her own concepts of it and the limiter release code, along with erasing her own memory of doing so. The failed Graviton Panel plan was just a ruse to make Gensei think he had won.
Chapter 69: Touma takes charge of the situation and has Gunha clear a path for him while he runs up to Mikoto. Her out of control powers obliterate his right arm, only for the dragon to come out and finally change her back to normal. His arm grows back and he nonchalantly says saving her was no big deal before covering her naked body up with his jacket.