Madonna was considered for the role of Catwoman/Selina Kyle in the 1992 film ‘Batman Returns’. She turned the part down and the role went to Michelle Pfeiffer.
In late 1996, a fifth Batman film, ‘Batman Triumphant’ was to start production for a projected mid-1999 release date. Madonna was reportedly going to play the role of Harley Quinn, who would be the Joker's daughter trying to get revenge on Batman for the his death. Due to the previous films, 'Batman & Robin', poor box office run and negative reviews from critics, ‘Triumphant’ was never made, and the film franchise went on hiatus for eight years until 2005.
Madonna also turned down another leading role in ‘The Fabulous Baker Boys’. Michelle Pfeiffer ended up winning the Golden Globe Award for Best Actress - Motion Picture Drama for her role. Madonna said that she felt the plot was "too mushy".
Sigh....