I feel Electro will actually make an appearance in one of these films! Just a feeling.
TASM-LIZARD
TASM 2-THE GREEN GOBLIN
Venom Spin Off (Maybe or after the third film)
TASM 3-THE SINISTER SIX
I know, it seems odd with the Sinister Six just popping up out of nowhere, but I think it would make an epic ending to the trilogy!
Tagline for the last film: The Ultimate Ending To The Untold Story

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But I also have the idea of...
TASM 2: THE GREEN GOBLIN
Plot: Peter and Gwen have broken up and they are still torn by the events from the year Peter was bit by the spider and fought against his mentor, Dr. Connors AKA the Lizard. Norman Osborn is brought into the story as a main character after seeing him with Dr. Connors in the Voult. He finds the destruction that OsCorp was left in. He's angered by this and blames Spider-Man. He uses the final draft of the formula Dr. Connors had used on himself and transfroms himself into a super being! He spies on Peter and plots his plan on destroying Peter's life.
Aunt May has introduced Peter to Mary Jane. Mary Jane and Peter date until Peter confesses to her that he still loves Gwen. Mary Jane agrees that it's probably better for him if he wants to be happy. She is completely fine with this. After he tries to go back to Gwen, she goes missing! Until, the Goblin tells Peter he has Gwen. Gwen has met her end!
Peter is left in complete anger! He goes on a manhunt for the Goblin and nobody is getting in his way!
He almost kills the Goblin, but stops himself and remembers what Uncle Ben had said to him long ago. The Goblin is killed by his own glider after he tries to kill Peter.
At the end, everyone is torn!
TASM 3: The Sinister Six
After six months, Peter is still left in grief. Mary Jane and Aunt May try to comfort him, but he always leaves. New super villains become present in New York as time goes by. To keep his mind off Gwen he looks through more of his Dad's old notes and finds an intresting paper titled "THE SUIT". He learns more about it. He faces the new super villain group, The Sinister Six. In college, Peter tells his friend Eddie Brock about the suit. Eddie is very fasinated by it and soon becomes obsessed with it, wanting to experiment on it all the time. Peter tries the suit and it feels awesome, but he's consumed by it and it makes him angry! Peter almost kills all the members until he rids himself of the suit.
Peter goes back to Eddie and tells him that it's dangerous and it has to be destroyed. Eddie is angered by what Peter is doing. He wants to know what power is! Luckily for him, he's been around the lab enough to know where an extra sample of the suit is. He uses it and is consumed by the power!
He has a final battle with the Sinister Six and they get their payback! Peter is for the fight for his life in the ultimate ending!
Venom Spin Off: Spider-Man (As Venom's enemy)
Eddie has gotten his hands on the suit and has plotted his plan to torture Peter! He makes Peter suffer and defeats him mentally and physically! But Peter is able to overcome and defeat Venom. Eddie is put in Ravencroft with Cletus Cassidy, until the symbiote comes for him, which sets up the Venom sequel!
***This is a rough draft so not all these will be the final thing!***
Forgotten plot points:
1. Peter and Eddie work at the Daily Bugle
2. Peter and Mary Jane begin dating again near the middle of TASM 3
3. The secret behind Peter getting his powers are revealed along with some other secrets throughout the 2nd and 3rd movie.