Yeah, Shokuhou Misaki. The other Level 5 in her School... She actually appears in the first episode of Season 2, and she's not a friend of Misaka Mikoto. She plays a big role in Season 3, and even the Manga arc that follows that.
She appears in Index second novel series: "New Testament" and she has a full arc dedicated to her there. So she's quite popular, and one of my favorite characters. (Not the top though.)