This news comes to us via CVG who has caught a retail listing for Diablo III on the European Amazon website. According to Amazon, Blizzard's next powerhouse is due out on April 17. This date, of course, hasn't been confirmed by Blizzard, who has only previously offered Q2 2012 as the release window for the game.
The official Battle.net website is currently listing a deal in which customers can get the game for free when signing up for a World of Warcraft annual pass. All signs point to a package just about ready for consumption.
Source: CVG, Amazon, Battle.net