Make Way for MJ
This definitely one of the best issues of Spider-Man and one of the most readable by today's standards. It lacks much of the cheesy vibe that many comics of that era give off, and the writing is excellent, portraying Spider-Man's grief exquisitely. And of course, it knocks off Gwen Stacy, who personally I've always found somewhat annoying. Spider-Man had many breaking points before this, but none so violent and finite, and this issue is a definitely read for those just skimming over the volumes.