The villain is going to be Jamie Foxx, who is now starring in the new Tarantino film Django Unchained. The new Spider-Man film is not due to be released until 2014, so of course there are many details we don't know yet, but we do know the villain is Electro as in the old comics and many other Spider-Man stories, games etc. In the first Amazing Spider-Man film, though, the villain was not Electro but the Lizard, played by Rhys Ifans.
Electro's superpower is the ability to control electricity, so we can expect some really dazzling special effects in the film. Jamie Foxx has talked a lot about the character - apparently he is going to look and be dressed rather differently from the old comic-book villain ( who traditionally appears in green and yellow), and the story about his origins may have been changed too in an effort to give him more of a 'real' personality.