Monsters vs. Aliens has the voices of Reese Witherspoon , Seth Rogen , Hugh Laurie , Will Arnett , Conrad Vernon , Rainn Wilson , Kiefer Sutherland , Stephen Colbert , and Paul Rudd . Monsters vs. Aliens features the voices of Reese Witherspoon , Seth Rogen , Hugh Laurie , Will Arnett , Conrad Vernon , Rainn Wilson , Kiefer Sutherland , Stephen Colbert , and Paul Rudd .