I don't know if anyone has posted this, and really, I don't feel like reading through 30 pages of this thread, but I also figure I should post in the Officially sanctioned Spider-Man 3 thread.
This is how I see the plot for Spider-Man 3 going down, and then the rest of the franchise after it.
We start off with John Jameson going off into space, one of the first things to happen in the movie. We then find Harry fiddling with the Goblin equipment, changing it slightly, either to Hobgoblin, or a more true to the comics Green Goblin costume. We also have Doc Connors working through his resaerch to grow back his arm. At some point he turns into the lizard. Maybe Spidey's fought Harry once or twice before this. Now he also has to deal with the lizard. Harry as the Green Goblin, somehow manages to always show up when Spidey has his hands full with the Lizard. He gets beat up pretty bad, manages to just barely get away from the fight for who knows what reason.
MJ gets really worried about him, doesn't want him fighting both the Lizard and the new Goblin at once, afraid he's going to die. That sort of thing, but he has to help the Lizard, because Peter knows it's really Doc Connors. He's been working on a cure for the Doc since he figured it out. Finally finishes the cure. Goes out to try and find Doc Connors.
At this point John Jameson's space shuttle crashes near Manhatten, a la the 90s Cartoon Series. Peter goes to the rescue as Spider-Man. Gets John out of the shuttle, goes in for the other crew members, as he goes in pumpkin bomb goes off, trapping him under some rubble. He tries to move it but can't. We vaguely see some strange dark shape shifting in the shadows. Harry, whom he doesn't know is behind the Goblin mask walks up then, with that spear like thing Norman had in the first movie, and sounding exactly like Norman says, "Goodbye, Peter."
Peter scrambles to try and get the piece of rubble off of him, but he can't. Harry's standing there over him, ready to strike him down. A few gun shots go off near Harry's head. He turns to see a few cops firing at him. He turns to Peter, "I'll be back to deal with you." Harry goes off to take out the cops.
Just then the dark shape comes out of the shadows, it's the black symbiote. It makes a tentative connection with Peter and tells him it can help him, if he'll let it. Peter not wanting to die, agrees. The symbiote merges with him and he throws off the rubble. The whole thing with the rubble of course to show us that the symbiote makes him stronger than he was before.
Peter and Harry then have their final battle ranging all over Manhatten, Peter really winning pretty easily. Even if/when the Lizard shows up. At some point, Peter is once again in danger of dying, maybe he's in a flaming building or something, hence why the symbiote can't help him. Harry suddenly realizes what he's doing and saves Peter's life. somehow taking a mortal injury himself. Peter unmasks the new Goblin to find out it's Harry. He's shocked. Harry's last words are, "Don't tell anybody." Keeping up the theme of the secrets that Peter must keep that's always been popping up in the movies.
If the Lizard showed up during this last fight, Peter manages to cure him, if not, that waits until the next movie, and the movie is now over. Or maybe it finishes with Harry's funeral.
Now we're on to Spider-Man 4.
If the Lizard issue wasn't resolved in the last movie it's resolved at the very beginning of this one. Or maybe that's the villian through the whole movie. The villian in this movie doesn't matter that much, it could be anyone. What matters is that Peter is wearing the symbiote and we see that he starts getting more and more violent as the movie progresses. I like the idea of the Lizard being dealt with early on, and then another villian or a stream of them being introduced in this movie, that Peter ends up dealing with more and more violently as the movie progresses.
Or it could be he's only dealing with Doc Connors, and it is his increasing violence towards Doc Connors as the Lizard that clues him in to the true nature of the Symbiote, as he doesn't want to hurt the Lizard.
Eddie Brock's hatred of Spider-Man is established in this movie, though perhaps he was introduced on screen in the last. Brock's hatred is the result of a macho moment that Peter has while under the influence of the symbiote, as he catches Brock taking pictures of him as Spider-Man and ruins Brock's film, to ensure his own financial well-being. Peter laments over what he did later on, unsure of why. At some point he realizes that the symbiote is evil. And he starts trying to find a way to get rid of it.
Perhaps he does this with the help of Doc Connors. In the end Peter gets rid of the Symbiote, possibly at the church bell, a la the comics. At the church that night the symbiote comes across Eddie Brock. The symbiote initiates a conversation with Brock. It learns how much Brock hates Spider-Man, and then tells Brock that it hates Parker, and reveals to Brock, that Parker is Spider-Man. Brock starts speaking in terms of "us" and "we".
Just then we get a cutaway of Peter waking up in the Spire and web slinging away to go back home. Then we cut back to Brock and the Symbiote who are now bonding. The movie ends with their bond complete and the birth of Venom.
Now Spider-Man 5.
Now we have an entire movie of Spidey versus Venom, with Venom having been properly established in the franchise with the proper background. Here's what we've all been waiting for, the grudge match. Perhaps we even some how have the birth of Carnage begun in this movie, I don't really care how it happens, or if it does. Movie ends with Spidey beating Venom, and Brock and the symbiote being seperated, and Brock getting locked up. If this is the last movie in the franchise let it end like that. If it's not, have Venom captured earlier in the movie, the carnage symbiote born at some point during his capture, possibly by scientists experimenting with the venom symbiote and trying to find a way to recreate it.
Movie ends with the venom symbiote finding its way back to Brock, and the two of them escaping together. And possibly the carnage symbiote finding a proper host who then also escapes.
Now here's Spider-Man 6, if they go this far.
Certainly here we have the carnage symbiote find a host and then escape to wreak havok on NYC. Spider-Man tries to stop him but he can't. Venom appears out of no where, he tries to beat Carnage can't. Carnage then runs off leaving his two beaten foes behind. Spidey and Venom agree to team up to beat Carnage, but Venom says it has to be on his terms. Spidey doesn't like the idea, but for now he agrees, wishing there was a better way.
They try things Venom's way for a while, but it just doesn't work out, especially because Spidey is reluctant to do things Venom's way. He's still looking for the other way. Suddenly, a la Maximum Carnage Peter realizes what the better way is, we are shown what truly makes a hero, and Spidey manages to beat both Carnage and Venom. And that my friends is the end. If I were Sony, that's how I'd do this franchise. But that's just me.