Memnoch
Lt. Vulture
Curiously, there's not much mention of Ian Holm's take on the matter.
I know it's been discussed before, but would he still be the obvious choice to fill the role of Bilbo? While it would tie in perfectly with LOTR, Mr. Holm is getting up there in age. Ian McKellan's reprisal as Gandalf is easier due to the prosthetics utilized but is Holms physically prepared for the physical demands?
I think I heard rumors that he may do it, but then he said he wouldnt due to the way they had to tape his face to make him look younger in FOTR, but then there came X3 with the age reversals of Sir Ian and Patrick Stewart so its anyones guess.