Whatever Sam Raimi does with John Jameson (if he does anything at all - I believe he and his brother just finished the first draft of the story he wants to tell), I can easily see him being one of the antagonists in Spider-Man 3. I think Raimi could do a decent job with Man-Wolf. He doesn’t even have to be a full-on villain like Green Goblin II/Hobgoblin, and M.J. could even be the one who takes him down in the end.
I’d like to see Peter and Mary-Jane’s relationship be relatively stable in the next film. Any angst in the third film should just be between Peter and Harry, and possibly Mary-Jane and John. No love-triangles. Peter may be uneasy with John’s feelings for Mary-Jane, but there should be no real threat to their relationship from John. She should just have to deal with protecting Spider-Man from John/Man-Wolf (who wouldn’t necessarily know Peter is Spider-Man - depends on his interaction with Harry).
If the Black Cat appears in a future film, it would cause angst in Peter and Mary-Jane’s relationship. Something I don’t want to see for a while. And I don’t think Black Cat would really be a full-on villain, so we’d have to see another true villain in a film with her. Venom would do nicely, since Spider-Man would likely need an extra hand (paw? ) to take him on. (Which would bother Mary-Jane in more ways that one.) Whether Venom is Eddie Brock, John Jameson or someone/something else, we’ll have to wait and see.
As for The Lizard, I don’t think Dr. Connors has been established enough to see him as a villain in the third film. I wonder if Dr. Stromm will show up again in the future? It would be really fun if Raimi threw in a small appearance by one of the D-list villains in Spider-Man 3. I’d like to see more of the wise-cracking Spidey, and laying the smack down onto some lame villain both physically and verbally early in the film would be cool.