I always thought that Louise Fletcher would make a great Mrs Johnson/Abigail. Check her out in Flowers in the Attic and picture her as Abigail, she's practicaly already playing Abigail there!
Nancy Barrett would also make a great Mrs Johnson/Abigail, I think she would be great with all that simmering passion subverted into insane religious mania. I'd be ok with her as Liz, I want one of the DS women to play her, I just think KLS would be better in that role.
I'd be cool with Joaquin playing Barnabas, or maybe Quentin. He'd be a better Barnabas I think, better suited for brooding than a bad boy.
Tim Curry would be great as Roger, but I think he'd make a fabulous Trask!
I always though Willian Shatner would make a great Sam Evans, I could easily picture him as a boozy failed artist with a doting daughter. James Franco could certainly play Joe, he has a quality that would make him believable as a salt of the earth hardworking fisherman.