Hermione saving Harry's ass by setting Snape's robes on fire. In truth, Hermione saved him by accidentally knocking over Quirrell on the way, who was enchanting Harry's broom. Snape was chanting the counterspell.
Harry catching the Snitch with his mouth.
Dumbledore's scene in the hospital wing with Harry.
Neville — the class klutz — standing up to his friends to protect the honor of his House. His only friends. It gets more awesome when you realize that Lupin and even Dumbledore, in similar situations, didn't have the courage to do what Neville does in his first year.And, this act ends up giving Gryffindor enough House Points to win the House Cup.
This turns out to be Foreshadowing of the final book, where he openly defies Voldemort himself!
Neville also jumping into the fray when Ron fought Malfoy. Neville took on the two physically strongest first years, at the same time and he held his own against the two long enough for Ron to give Malfoy a black eye.
The poke of death!
Lily's sacrifice. Voldemort wasn't even going to kill her in the first place, but she offered herself instead of her son, got killed first, and essentially defeated Voldemort by protecting her son.
"I think I can tell the wrong sort for myself, thanks."
Harry frightening Peeves away by impersonating the Bloody Baron.
Dust-Voldemort trying to kill Harry. Scary as hell? Yes. Completely awesome? Hell yes!
When Quirell was warning about the troll and fainting and the students begin to panic and run amok, Dumbledore stopped them simply by shouting "SIIIIIIIILENCE!!!. Before calmly instructing the teachers and prefects on how to deal with the situation. Unlike the later example, he didn't even need a wand to make his voice heard.