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Dead Island is on sale for $11.99 (60% off) at Green Man Gaming. Use the 10% off voucher code ROYAL-BARGA-INING to get the game for $10.80. It uses Steamworks so you’ll have to activate it on Steam.
You can also get the Rhyder White and/or Bloodbath DLC for the game for $3.60 after the 10% off voucher code.