Bestival released a mobile app for iPhone and Android. It's £2.99 and you can get more info about it here. Also, here's the tentative lineup listed for the Main Stage on Sept. 10th:
The Cure / Rob Da Bank / PJ Harvey / Ross Allen / Crystal Castles / Grandmaster Flash / Paloma Faith / Jaguar Skills / Village People / Rev Milo Speedwagon / Katy B / MistaJam / Toots & The Mayals /
Bestival FM / Claire Maguire / Bestival FM / Mr Motivator / The Ukelele Orchestra of Great Britain.
(Thanks to kersh2099 for posting it on the Sunday Best forum)
Update: Festival site map here, and stewpotty's Google Maps version.