So many good ones. Where to begin? Are you looking for good one issue stories or parts of an ongoing series?
There are tons of good one off issues where the story wraps up nicely. Many of the 60-70s issues of ASM were one off. The Vulture, Green Goblin, Lizard, Doc Octopus, Scorpion, Electro, etc. all feature prominently. Later there were some great crossover stories as well.
The Night Gwen Stacy Died is an important issue in the series, but so is issue #129 The Punisher is introduced or the one introducing Morbius #101 or some of the ones with the black alien suit.