Nipples on the Batsuit.
BBC news had a report a few days back where a Sony movie exec confirmed Spider-Man movies will be coming out until the Apocalypse (or whenever they run out of "good stories"). :-)
Over at Freeze Dried Movies they have a source that says that the villains for Spiderman 4 will be the Lizard (aka Doc Connors, Peter's college professor, who's appeared in all three movies so far) and... Carnage. For those of you not aware, Carnage is like Venom on steroids. The word is that the next film would have to be "darker" to accomodate the Carnage character.
Darker than Spider-Man 3? And after the great (*cough*) job they did with Venom in this one?
I suppose you can go pretty dark in a PG-13 movie (look at the progressively creepier Harry Potter movies), but Spider-Man appeals to the little kiddies all the way down to kindergarten. In the comics, Carnage is a serial killer. Great stuff to bring little Timmy to, don't ya think?
Also, since three antagonists worked so well in this movie, there's also talk of adding Black Cat to the mix for the next film.
Finally, although Raimi stated a few weeks ago that he might be up for number four, the studio has said that the franchise could go on without him, Kirsten Dunst or Tobey Maguire. The vibe from various interviews is that they'll do it as a team or they won't do it at all. It wouldn't be the first time that a movie studio replaced directors and lead actors in a superhero franchise. They did it quite successfully with Batman Begins and they're in the process of doing it with The Incredible Hulk.