THR reports that Irrfan Khan ("Slumdog Millionaire") is in discussions to join the cast as the villainous Nels Van Adder (THR calls him Van Atter for some reason). He's not a very well known nemesis to Peter Parker. In the comics, Van Adder is an employee of Osborn Industries who is one of the subjects of Norman Osborn's experiments and turns into a red, demon-like being known as the Proto-Goblin (this is before Norman would turn into The Green Goblin). His transformation gives him large claws, talons, fangs, glowing green eyes, and nearly bulletproof skin. Thank you comic reference sites.
Meanwhile, the rest of the cast is being padded out by thespians Campbell Scott and Julianne Nicholson ("Law & Order: Criminal Intent") who will play the parents of Peter Parker, while Annie Parisse ("Rubicon") will play Nels Van Adder's wife. There's no word yet on how Parker's parents will factor into the film -- flashback? prologue? -- but it's an interesting bit of casting as they've never factored too heavily in comics or in Sam Raimi's trilogy.
The quartet join a strong cast that currently includes Andrew Garfield, Emma Stone, Sally Field, Martin Sheen, Rhys Ifans (as the other villain, The Lizard) and Denis Leary. Filming starts very soon on the reboot and it will sling its web into theatres on July 3, 2012.