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.
And let's not forget Neville also jumping into the fray when Ron fought Malfoy. True, Crabbe and Goyle kicked his ass, but it's the principle of the thing. 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. That's more than a principle.
The poke of death!
What about Lily? 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.
Harry frightening Peeves away by impersonating the Bloody Baron.