I'd like to see them combine the characters of Victor Zsasz (spelled Zsaz in 'Batman Begins') and The Riddler into one, and have him be a Zodiac-style serial killer who taunts the GCPD and Batman with letters hinting at his next crimes in codes and riddles. This would allow the movies to continue to reference back to the earlier films (as the Joker was in TDK) and would allow Batman to take on more of a detective role as in the comics.
Have Zsaz be an amnesiac due to experimental treatments and repeated exposure to the Fear Toxin by Dr. Crane/Scarecrow at Arkham. As a result of his memory loss, in addition to carving hash marks on his body for each of his victims, he also carves question marks into his skin and the skin of his victims. Though his intellect is fully intact, the riddle of his own past drives him to adopt the Riddler persona and to frequently ask "Who is the Riddler?"
They could bring back musician Tim Booth to reprise his role from the first film, but personally I'd prefer a bigger name for the role, and I can think of no one better than John Malkovich, both for his resemblence and for playing a psychopath so very well on several occasions.
That being said, if they don't go in that direction, Robin Williams is a great dramatic actor and movie psycho as mentioned above, I just don't see him being much of a physical threat to Bale's Batman. Despite the Riddler's more intellectual modus operandi, it's inevitable in these films that the protagonist and antagonist will have a physical showdown at the end.
Other actors who would be good in the role include Kevin Spacey (he hasn't played a mass murderer in a while) and Viggo Mortenson.
Have Zsaz be an amnesiac due to experimental treatments and repeated exposure to the Fear Toxin by Dr. Crane/Scarecrow at Arkham. As a result of his memory loss, in addition to carving hash marks on his body for each of his victims, he also carves question marks into his skin and the skin of his victims. Though his intellect is fully intact, the riddle of his own past drives him to adopt the Riddler persona and to frequently ask "Who is the Riddler?"
They could bring back musician Tim Booth to reprise his role from the first film, but personally I'd prefer a bigger name for the role, and I can think of no one better than John Malkovich, both for his resemblence and for playing a psychopath so very well on several occasions.


That being said, if they don't go in that direction, Robin Williams is a great dramatic actor and movie psycho as mentioned above, I just don't see him being much of a physical threat to Bale's Batman. Despite the Riddler's more intellectual modus operandi, it's inevitable in these films that the protagonist and antagonist will have a physical showdown at the end.
Other actors who would be good in the role include Kevin Spacey (he hasn't played a mass murderer in a while) and Viggo Mortenson.