Martin Freeman appears to be set as Bilbo, which gets a big thumb's up from me. And I didn't even like the movie version of Hitchhiker's.
The other names also floating around as potential cast members, though, are a bit more interesting. In order of geeky magnitude:
- David Tennant (everyone but me's favorite new-school Dr Who). The only part he would make sense for, to me, is that of Elvenking Thrunduil, ruler of the wood elves of Mirkwood -- and Legolas' dad.
- Michael Fassbender (the British spy from Inglorious Basterds). I can see him best as Bard, but Beorn could also be a possibility...
- ...except that Jekyll star Jimmy Nesbitt is also on the list, and if he isn't born to play a werebear I dunno who is. I guess you could shrink him down to dwarf size too, but that seems a waste.