Easy one for me to answer. My favourite game of all-time.
2002, Round 2, Leafs & Sens. Sens had taken game 5 on a brutal non-call on a board from behind by Alfredsson on Tucker. It was hugely demoralizing to the badly injured Leafs. The Sens had game 6 at home. They scored two goals early in the 1st, and their stupid annoying horns were blaring louder than ever. Then Domi got hit by Ricard Persson, who got 5 and a game. Domi was against the boards and I am sure he allowed himself to fall easily on the dasher to make it look good. The Leafs scored one on that PP, and got momentum back. They eventually went up 3-2, then Todd White scored on what I believe was a breakaway. Finally, on a harmless looking play that looked like it was leaving the Ottawa zone, Travis Green stole the puck and fed Mogilny, who was still deep in the zone, and he made no mistake. 4-3 Leafs. They held them off the rest of the way and won game 7, 3-0.
Gretzky's 1993 performance against the Leafs deserves mention, too. He had a bit of help from the refs, of course...