I'm putting my money on Vulture and Electro.
-Raimi expressed interest directly in those two guys in particular.
-The various strands of news seem to make a stronger case for Vulture than Black Cat (villain buys Daily Bugle, said villain has daughter that many actresses are auditioning for, definitely sounds more like Vulture-Valeria than Black Cat-"Villain Artificially Forced to be Her Father")
-They wanted to use Vulture in the last movie, and already pegged Ben Kingsley for the role. They may very well want to make up for that now.
-They said they were casting a male villain role. If Ben Kingsley is already pegged as Vulture, and they still need to cast the other one, that makes sense.
-The special effects dynamics make sense as something they would do. Vulture as the aerial villain, Electro as the super-powered, eye-candy villain.
-The character dynamics between the two would be great. Vulture as the intelligent, urbane, villainous mastermind--Electro as the simpler-minded, neurotic, unstable protegé... one who realizes how much more powerful he is than his master, and turns on him.
-Shoving Black Cat in there seems like a bad idea after Spider-Man 3. She's basically half a villain, so Black Cat and two villains is 2.5 villains (a repeat of Spider-Man 3), and Black Cat and one villain is 1.5 villains--which is unsatisfactory, especially if the other villain is the Vulture. The Vulture by himself would be pretty lame. 1.5 villains might have worked if the main antagonist was Doc Ock, but not with any of the guys we have left. Two solid villains seems like the best way to atone for Spider-Man 3.
So, predicting, and hoping for, Electro/Vulture, with all of these actresses auditioning for Valeria, not Black Cat.