My choice was always Parker for this, as well.
But you never know... maybe there's someone who's great in a different genre just wiating to get his/her hands on a musical.
Before Dancer in the Dark, Lars Von Trier was about the LAST director I'd have thought would be interested in musicals. Not that he'd be very good for Les Miserables, but it just goes to show...
This is just bound for controversy, but Paul Thomas Anderson has some of the ingredients that could work:
He's got an affinity for music and knows how to tie it in to the plot, he's great at juggling multiple subplots, he's got enough clout to generally get final cut (which would be essential for something of this scope), and he's got a knack for the kind of happy/sad dynamic that you get from Les Miserables. Not to mention, he's got a thing for singing, waif-like girls.

Of course, it would also be a sort of non-personal project, and that would be out-of-character.
And I've said it before, and I'll keep saying it: Tom Waits as Thernardier.