The Jackal was a decent if not especially memorable 70s Spider foe who later became infamous when he (and his most famous storyline) were resurrected as the basis for the legendarily bad "Clone Saga". Warren is a science teacher who was nursing a crush on his student Gwen Stacy. When she was killed by the Green Goblin, he went nuts and invented cloning in order to bring her back to life by funding his experiments with crimes committed while disguised as a green jackal-man. I elaborated on what came next here. It actually makes a lot of sense for him to show up in this new movie series, given the emphasis on super science and the presence of Gwen Stacy.
Now THIS would be interesting. Ezekiel is an aging, wealthy businessman/philanthropist who has the same powers as Spider-Man, except he gained his through ritual totemic magic. In lengthy early-2000s story arc, Ezekiel tells Peter Parker that his spider-powers are magical, too; the radioactive spider meant to bite him and pass on these abilities. He helped Peter battle a series of Spider-Totem-hunting threats, but it turned out they were really after Ezekiel, who'd been trying to position Peter as a fall guy sacrifice. It's actually not quite as bad as it sounds, though a lot of bad story turns eventually spun out of it.
Silvermane is a mafia boss, who is later a slightly more interesting cyborg mafia boss. In his first appearance, he forced Curt Connors to synthesize a youth potion from a formula on an ancient tablet ... which winds up turning him into a baby, and then later an erratically aging adult requiring cybernetics to stay alive.
If you don't know who this is, you probably aren't reading this article.
Studio publicity doesn't always tell the truth, and actors are not always in the loop as to script/production decisions. In other words, even though it's been "denied," I'd still call this the most likely candidate.
Hear me out on this one.
Something seems to be missing from The Amazing Spider-Man. Almost all of the trailers include a line of dialogue where someone (Connors?) asks Peter Parker if he thinks what happened was really an accident and if he knows what he "really" is. The whole re-imagined back story is all about setting up some conspiracy mystery in the deaths of Richard and Mary Parker, a conspiracy that Curt Connors, the rival OsCorp scientist played by Irfahn Kahn, all seem to have intimate knowledge of. And yet, none of it actually seems to involve any secret about Peter himself, and the "what you really are?" dialogue doesn't appear in the film. Also, Kahn's character vanishes midway through.
What happened? Well, according to web gossip as fresh as two months ago the film was originally going to make a much more dramatic change to Spider-Man's origins. Richard Parker would've been revealed to have tested the Secret Formula stuff on himself and passed the genetic-changes to his son Peter, and these already latent abilities would've been "activated" by the spider-bite. In other words, the same reworked origin from the Ang Lee Hulk movie.
The studio never confirmed or denied this rumor, but if it was there and hacked out at the last second (it's said that there were reshoots after test screenings) it explains an awful lot. The super science holy grail Connors and others are seeking on behalf of Osborn is the ability to successfully cross animal and human DNA, and while Connors can pull it off, he can't stabilize it - hence The Lizard. Peter, on the other hand, was able to absorb spider traits without turning into a Spider which, in the film, is never adequately explained. But if Peter is carrying the stabilizing agent in his own blood, that not only explains the powers but also gives cause for Osborn etc. to chase him down in the sequels.
Meanwhile, who knows what really became of Richard Parker, if he indeed tried the stuff on himself. If they were already going to snag the ill-advised genetic legacy business from Hulk, why not also steal the ill-advised "Hero's-Dad-as-Evil-Version-of-Hero" stuff as well?