This is one casting rumor that has become a reality.
After weeks of speculation, Dominic Monaghan has officially joined the cast ABC's FlashForward. Not much is known about his character at this time, except that he'll be named Theo and will show up on the drama's second episode.
Monaghan made his name in the Lord of the Rings franchise; and then shot to television stardom as Charlie on Lost.
He still may appear on that show's final season, as both Lost and FlashForward air on ABC. The network, in fact, is hoping the latter fills in nicely once the former goes off the air, as each series centers around mysterious events and characters.