New X-Men (Morrison) - People....
Fantastic Four (Lee+Kirby) - My absolute favorite run on a comic ever. Jack and Stan just brought out the best in each other. Without this book superheroes would be the perfectly perfect people they were at DC. This book built Marvel from the ground up and set the tone for decades to come. I personally feel it should be #1.
Uncanny X-Men(Claremont) - If any run was going to beat my beloved Kirby/Lee FF this was the one. It changed so many thing and brought what was a C-list team of heroes into the forefront of Marvel. Claremont may have lost a lot of his spark but when he was on dear god it was good. And I'm not even an X-fan.