According to the site, David Oyelowo (Lee Daniels' The Butler) - who has also been rumoured as a potential addition to the cast of Episode VII - Freddie Prinze Jr. (Scooby-Doo), Vanessa Marshall (Justice League: The Flashpoint Paradox), Taylor Gray (Bucket and Skinner's Epic Adventures), and Steve Blum (The Avengers: Earth's Mightiest Heroes) are set to lend their voices to the series, although as yet there's no details on any particular characters.
Star Wars: Rebels will be set between Revenge of the Sith and A New Hope, and will be executive produced by Simon Kinberg (X-Men: First Class), Dave Filoni (Star Wars: The Clone Wars), and Greg Wesiman (Young Justice).