Though I can't say I'm an expert on the subject/series, according to the IMDb there is slated to be a new Dr. Mabuse installment in 2010, which will hopefully do well and get an American release. This is one horror/espionage/serial figure that could use an update, what with all the conspiracy theories, social unrest, and the like nowadays (Not sure about what the tone is in Germany at the minute)... A new "Mabuse" would be great even if it won't have the same imagery Lang put in the first two.
http://www.imdb.com/find?s=all&q=dr.+mabuse (http://www.imdb.com/find?s=all&q=dr.+mabuse)
http://www.filmbuffonline.com/FBOLNewsreel/wordpress/?p=323 (http://www.filmbuffonline.com/FBOLNewsreel/wordpress/?p=323)
Actually, this could be really cool if done right.