While she's no pushover before this, her first jaw-droppingly kick-ass moment has got to be when she defeats the entire Sound Team by herself, killing all three of them without flinching until the threat to her teammates is over. Then when Sasuke is possessed by the Curse Mark, she takes a strike to the chest, which snaps him out of hispower-trip.
Using the Substitution Technique with only a moment to spare to switch with Sasuke, taking Itachi's Tsukuyomi full-force.
Defeating Kidomaru, with Kiba and Akamaru backing her up. And given that Kidomaru shrugged off Ino's Signature Move, it makes her triumph all the more savoury.
All the various stages of that two-chapter fight deserve mention, actually, including a meta-example in praising the author for constructing it so well despite that "the fight scenes are killing [her]".
Naruto curb-stomping Neji, during the Chuunin Exam Finals. Made even better because it came about as a result of Shikako mentoring him in a way which kept him interested, and raised his intelligence several notches compared to canon.
In Ino's fight against Temari in the Chuunin Exam Finals, she manages to disarm her opponent which - given Temari's reliance on the fan for her Wind-based techniques - leaves her weakened despite defeating Ino, and so she becomes easy pickings when the Invasion breaks out. Offset somewhat by Ino not preparing for her opponent being strong without her weapon, which leads to her being denied a promotion.
Shikamaru and Shino's fight in the Chuunin Exam Finals. Seeing two of the best strategists in the series duke it out in their incredibly subtle manner(s) is highly impressive, and barring Naruto and almost Shikako (who didn't even make it to the Finals, but was praised for her deductive reasoning), they're the only ones receiving promotions when all is said and done.
In the Sasuke Retrieval Arc, Hinata of all people pulls a Big Damn Heroes - and then uses her new move against Kimimaro in the process:
Hinata: "Protection of the Eight Trigrams; Sixty-Four Palms".
Followed by Lee, Naruto, and the Sand Siblings each making their own, in that order.