I know it's unlikely considering that all of the characters are liscenced to different studios but a fourth movie that kept things fresh and interesting could only generate the 'hype machine' and anticipation by having a crossover between characters. One I could definitely see would be Spidey and the X-Men. It really wouldn't ruin anything to have characters believed dead to return with a one liner explanation. I could see Spider-Man going to consult Xavier for something... it would work well and be highly marketable. Even just Spidey and Wolverine would work since those characters have great chemistry with each other. I don't think SM3 would be as anticipated by the general public as it is without having the 'new costume' and 'darkness' to it. If a fourth movie returns things to the status quo it could only be as good as SM2 was. Thoughts on the crossover idea?