I posted about this on the Musicals.Net board. It's gotta be a difficult line to tread...they want actors with some screen presence, but who can handle this material.
I'm not crazy about the idea of Russell Crowe as Valjean, but then, I've never heard him sing. Hugh Jackman, I think, would make a better Valjean than a Javert.
As for Javert...Brian Stokes Mitchell. He straddles the line between stage and screen, his name is well-known enough, and the voice, the voice, MY GOD THE VOICE. (And Javert's supposed to be gypsy or half-gypsy, so having a darker-skinned Javert would be a nice shout-out to the Brick!)
Someone on Musicals.Net raised the possiblity of Ewan McGregor as Thenardier, and I think I agree! He's got a good voice for that particular part, and on the strength of his past roles, can do justice to the two sides of Thenardier--the roguish comic relief and the sinister, unsettling predator crawling around in the sewer robbing corpses. Otherwise, Hugh Laurie would be great, and so would Alan Cumming.
I adore Christian Bale, so what role is he both age-appropriate and voice-appropriate to play? I'd suggest Javert, too, if it wasn't already taken.

A little old for Enjolras...oh, well, I'll think of something.
If they cast some roles with major names, then maybe they can get away with raiding the various casts for the best of the best to play the rest of the roles.