The Sinister Six is headed by Doctor Octopus, including other Spider-Man foes Sandman , Kraven The Hunter, Vulture, Electro and Mysterio. The Six banded together as they have realized they can't singlehandedly defeat Spidey by themselves.
Alfred Molina, the actor who played "Doc Ock" in the first film, expressed his interest in Sinister Six. Here's an interview with Collider (via totalfilm.com):
"That was the most fun I think I've ever had on a movie of that kind, you know, those big, big sort of features where you spend like six months hanging off a wire, you know, and that stuff. But it was the first movie of that kind that I've ever been involved in. I had a wonderful time. I loved it. I mean, I'd go back and do it again in a heartbeat."
"It was the first movie of that kind that I'd ever been involved in," he continues. "I had a wonderful time. I loved it. I mean, I'd go back and do it again in a heartbeat."
He also added that no one owns the roles in the movies, especially Spider Man with Garfield replacing Maguire.
"The thing is, no actor owns those roles." "Maybe they'll come after me for Doc Ock ... how about Doc Ock's evil twin?"
A Venom solo movie has been reported to be in development, to be directed by Alex Kurtzman. Here's an update from the director himself of the upcoming movie (via Screen Rant):
"Yeah, before last Friday came out, we started kind of roughing out a story. Ed Solomon's going to be writing it very soon. I can't tell you too much, but I'm really excited about it.
I would not say [picking the incarnation of Venom is] an easy choice. I would say that there are quite a few things about Venom that are interesting. Venom had several different iterations, and there are several things that are very unique, interesting and specific.'"
Also a few weeks ago, Warner Bros. also announced that they have greenlit their take of a villain-centric film, Suicide Squad, a team formed to tackle top secret missions to lower their sentences. The "Squad" includes Batman's villains Deadshot, Bronze Tiger, Deathstroke, Captain Boomerang, Count Vertigo and Harley Quinn.
Confirmed actors that have signed on to Suicide Squad are Will Smith, Wolf of Wall Street's Margot Robbie, Jai Courtney, Tom Hardy and Jared Leto, who will be taking on the role as the new Joker.
The Suicide Squad will showdown with Sinister Six with both films having a 2016 release date, potentially starting an influx of villain-centered films.