Amazing Spider-Man: One More Day
Written by J. Michael Stracynski
Takes places in Amazing Spider-Man # 544, Friendly Neighbordhood Spider-Man #24, Sensational Spider-Man ##41 and Amazing Spider-Man #545.
Peter's Aunt May is shot by a bullet intended for Spider-Man. During most of the story she is in a coma and Spider-Man/Peter Parker searches for a way to keep her from dying.
In the end, he strikes up a deal with Mephisto who agrees to bring her back, in exchange for Parker allowing him to alter time so that he and Mary Jane were no longer married.
It's a good story but that fact that it screws up years and years of Spider-Man continuity is kind of irritating.