When Bennett Brant's return from the dead came up in the thread about why Jean DeWolff, Ben Reilly and Ned Leeds aren't mentioned more often, I was struck by how often "normal civilian" supporting characters were transformed into something else or became connected to superheroes and villains, so that these days there are precious few recurring characters who 1) did not gain superpowers themselves or 2) are related to a supervillain or -hero. I'll attempt a list:
Liz Allan - revealed to be the Molten Man's step-sister in the 1970s, later married Harry Osborn (Green Goblin II), bore his son, and between the Clone Saga and BND was Norman Osborn's (Green Goblin I) daughter-in-law.
Flash Thompson - became the new Venom after OMD.
The other students at Midtown High (mostly used in crowd scenes): Sally (Avril) in Untold Tales of Spider-Man became a costumed heroine and was later killed. At least two other students who attended Midtown High at the same time as Peter gained superpowers: Jessica Jones (Alias) and Charlie Weiderman (in "Skin Deep" during JMS's run).
J. Jonah Jameson - Father of John Jameson, who became the Man-Wolf. JJJ is also responsible for Mac Gargan becoming the Scorpion and funded several Spider-Slayers (at least one of which was built by his later wife, Marla Madison).
John Jameson - became the Man-Wolf.
Betty Brant - her brother Bennett was brought back from the dead and retooled as the new Crime Master in the Venom series starring Flash Thompson.
Frederick Foswell - became the Big Man, later was killed.
Ned Leeds - was for a time believed to have been the original Hobgoblin. In any case, he was killed off.
Mary Jane Watson - was married to Spider-Man between ASM Annual #21 and OMD.
Gwen Stacy - was killed off and decades later revealed to have been the mother of Norman Osborn's twin children, who are also superpowered.
Professor Warren - became the Jackal, died, was replaced by his clone Carrion, who also died.
Sha Shan - I vaguely recall that her grandfather was some kind of priest/mage who was somehow connected to Dr. Strange. She also used to be the villainess Sister Sun, partnered with a certain Brother Power.
Jean DeWolff - daughter of a criminal father, sister of the Wraith.
Marcie Kane - revealed to be an alien, left Earth.
Ben Urich - uncle to Phil, who later became a new Green Goblin and Hobgoblin.
Hector Ayala (one of Peter's fellow teaching assistants) - became/was revealed to be the original White Tiger.
Which basically leaves as notable "normals" (among the living):
Aunt May (although she used to be Doc Ock's fiancee)
Aunt Anna Watson (and the other Watson relatives)
Joe Robertson and his family
and some minor characters, most of whom haven't been seen in ages (e. g. Roger Hochberg, Mrs. Muggins, Randi, Bambi and Candy...)
Any additions and/or corrections?
Um, Glori Grant is still around, isn't she? And what about that female photographer that used to be a supporting cast member? Kate Cushing, I believe, was her name. Ben Urich, but he's usually associated with Daredevil, and with the Daredevil universe. But we always get new supporting cast members.