I totally agree w/what you said about Ashley Judd, I loved the book, I didn't even see the movie, it was so wrongly cast (Natalie Portman as white trash? no.)
Another one that comes to mind is Barbara S. as Dr. Lowenstein in "Prince of Tides", she did a good job directing, but I thought she was wrong for that character.
I also HATED Mia Farrow as Daisy in "Gatsby".
On a positive note, some of the BEST castings ever were:
Harry Potter
LOTR