Barring any unforeseen last minute disruptions in the hiring process, Pearce will join Robert Downey Jr., Ben Kingsley, Gwyneth Paltrow and Don Cheadle in the first post-Avengers film, per Variety. Production is gearing up now to get underway in North Carolina next month.
The character Aldrich Killian is from the Warren Ellis-written limited series Iron Man: Extremis, the same series that provided inspiration for the first Iron Man film's origin story and its sequel's briefcase armor. Killian figures heavily into the Extremis plotline which would seems to confirm rumors that Tony Stark's next adventure will see him caught up in the world of nano-technology. The Extremis storyline also has strong ties to the Super Soldier syrum that created Captain America, more specifically the chase to recreate the serum in modern times.
You can go find out more about Iron Man: Extremis and potentially get a good idea of where Robert Downey Jr. will next be headed by Googling it.
As for Guy Pearce, he's quickly attached himself to two of the biggest movies in this year and next. You'll see Pearce in the ensemble Sci-fi horror thriller Prometheus in June, then in May 2013 Iron Man 3. It's good to be Guy Pearce right about now.