The corporate giant has said before how it will only bundle them with Special Edition Xbox 360s. They told big fibbers though - no pricing yet.
Online retailer Amazon.com has already listed the latest Xbox 360 accessory but haven't posted up a price to go with it. As Joystiq points out, it's quite odd to see such a product spillage from the official dashboard itself.
Has hard drive space been a problem for you? It's also been revealed recently that the Xbox 360 will open up to USB devices for storage with an artificial limit of 16GB and two connected devices at a time, thanks to a planned dashboard update.
UPDATE: Microsoft has issued the following press release:
Available in stores today, Xbox 360 introduces the 250GB Hard Drive, which offers more space to store your favorite game and entertainment content. Available at the incredible value of $129.99 (U.S ERP), the 250GB Hard Drive offers more freedom to download the latest demos, Xbox LIVE Arcade games, full game titles with Games on Demand, TV shows, movies and more straight to your Xbox 360 console.
Xbox LIVE is the premier destination to download the best games and entertainment at the touch of a button, 24x7. With a growing library of more than 13,000 pieces of gaming content, and more than 25,000 movies, TV episodes and music videos available to download or stream instantly – you’re bound to find something you love.
Want to express your personality and style on Xbox LIVE? With the added storage space of the 250GB Hard Drive, it makes it easy to download and save new Avatar clothes and props from your favorite clothing brands and games, including Roxy, Quiksilver, Adidas, tokidoki, “Halo,” “Gears of War” and more. Or, download a pet to keep your Avatar company.
More detailed information can be found at www.xbox.com.