Santigold and Hercules and Love Affair will play the Thursday date of the festival, which runs from September 8 to 11.
Other acts announced to be playing the first day include Mirrors, OneTwo and Blancmange on the Back To The Phuture stage.
They will be joined by DJ sets from Richard X, Arthur Baker and Mark Jones.
Bestival 2011 will be headlined by Pendulum, The Cure and Bjork. The festival will take place at Robin Hill Park on the Isle of Wight.
Tickets are on sale now.
Bestival will become one of the first music festivals in the world to be broadcast in 3D when it airs on Sky 3D in September.
Watch the music video for Santigold's 'Say Aha' below: