Microsoft/MSDN

MSDN
"The Microsoft Developer Network (MSDN) is the portion of Microsoft responsible for managing the firm's relationship with developers: hardware developers interested in the operating system (OS), developers standing on the various OS platforms, developers leveraging the API and scripting languages of Microsoft's many applications." (Microsoft Developer Network - Wikipedia)

Buy an MSDN Subscription - http://msdn.microsoft.com/en-us/subscriptions/buy.aspx

As of 2013.01.22:
 * MSDN Operating Systems - $699.00 ($499.00 Renewal)
 * Visual Studio Professional with MSDN - $1,199.00 ($799.00 Renewal)
 * Visual Studio Test Professional with MSDN - $2,169.00 ($899.00 Renewal)
 * Visual Studio Premium with MSDN - $6,119.00 ($2,569.00 Renewal)
 * Visual Studio Ultimate with MSDN - $13,299.00 ($4,249.00 Renewal)

Library
MSDN Express Library

MSDN Operating Systems
MSDN Operating Systems is available as a standalone purchase.

MSDN Operating Systems ($699)

Buy, renew, or upgrade an MSDN Subscription through Microsoft or a qualified reseller | MSDN Subscriptions

Volume Licensing (VL)
"Volume License key (VLK) is a term used by some computer software companies to denote the product key used when installing software licensed under volume licensing, which allows a single product key to be used for multiple installations" (Volume license key - Wikipedia)