From The Hollywood Reporter:
Set in an alternate America, "Watchmen" follows costumed hero Rorschach, who is living a vigilante lifestyle because most masked heroes have retired or been outlawed. While investigating a murder, Rorschach learns that a former masked-hero colleague has been killed, prompting him to begin investigating a possible conspiracy.
Jackie Earle Haley - Rorschach
Jackie Earle Haley will play Walter Kovacs, aka Rorschach, who ignores the ban on costumed vigilantes.
Billy Crudup - Dr. Manhattan
Billy Crudup will play Dr. Manhattan, a superpowered being with godlike powers and temperament.
Malin Akerman - The Silk Spectre
Malin Akerman will play Laurie Juspeczyk/the Silk Spectre, who is involved with Dr. Manhattan -- but that relationship begins to fall apart as he becomes more disconnected from humanity.
Matthew Goode - Ozymandias
Matthew Goode will play Adrian Veidt/Ozymandias, a costume adventurer who retired voluntarily, disclosed his identity and built a large fortune. He hatches a plot to avert a global catastrophe he believes will be caused by Dr. Manhattan.
Patrick Wilson - Nite-Owl
Patrick Wilson will play the Nite-Owl, a crime-figher who uses technical wizardry and has an owl-shaped flying vehicle.
Jeffrey Dean Morgan - The Comedian
Jeffrey Dean Morgan will play the Comedian, a cigar-chomping, gun-toting vigilante-turned-paramilitary agent.
Stephen McHattie - Hollis J. Mason (Night Owl I)
Stephen McHattie will be playing Hollis J. Mason (Night Owl I), a long since retired superhero who lends his name and likeness to Patrick Wilson's character.
Carla Gugino - Sally Jupiter (Silk Spectre I)
Carla Gugino will be playing Sally Jupiter (Silk Spectre I), a burlesque dancer-turned-costumed heroine and sex symbol the Silk Spectre who is part of the Minutemen, a group of heroes who preceded the Watchmen.