This page is a placeholder, and will contain the Windows 8 and 8.1 Digital River download links should they become available. Until this is the case, you can find some alternative sources for Windows 8 here. I keep monitoring the Digital River servers using a scraping script, and as soon as Windows 8 turns up, this site will be updated.
Windows 8 on Digital River
I'm monitoring the download domain digitalriverconten.net closely, and have a crawling script search for Windows 8, Office 2013 and other downloads regularly. As soon as the iso files turn up, you'll be able to find them here. A recent complete scan of Digital River due to the release of Windows 8.1 has revealed no further downloads.
Up until recently, there was a notice on windows7.digitalriver.com that the Digital River Windows Store has closed down. Now even the subdomain isn't available any longer. It seems that Microsoft wants to distribute Windows 8 exclusively through their own website. This raises some doubts whether Windows 8 installation media will be available for free download like Windows 7 and Windows Vista before.
Windows 8 left-over lot on Amazon
If you prefer to hold a physical disk of Windows 8 in your hands, you can get one from the leftover stock of the initial upgrade offer at Amazon. This version can be upgraded to Windows 8.1 free of charge. In fact, this option is much cheaper than purchasing a full version. Microsoft stopped distribution of the initial offer on 31 January 2013, but Amazon still seems to have some stock remaining:
Windows 8 Test Drive
If you don't want to spend any money now, but still have a look at the final release of Windows 8.1, you can download a 90 days evaluation version of Windows 8.1 Enterprise. The previous release Windows 8.0 is also available for evaluation. Windows 8.1 Enterprise from Microsoft.
After the 90 days are over, these versions can't be converted to a full product by entering a purchased product key.
Install now, Activate later
In previous versions, it was possible to install Windows without key, run it as trial for up to 120 days, and enter a product key later. This option on first sight seems to have been removed in Windows 8.
However, it's still possible to pre-install Windows 8 or Windows 8.1 with a generic key. These keys can only install Windows. It's not possible to activate it unless you enter an original key purchased from Microsoft. Here they come...
XKY4K-2NRWR-8F6P2-448RF-CRYQH (Windows 8 Professional)
RR3BN-3YY9P-9D7FC-7J4YF-QGJXW (Windows 8 Professional with Media Center)
FB4WR-32NVD-4RW79-XQFWH-CYQG3 (Windows 8 [Home])
XHQ8N-C3MCJ-RQXB6-WCHYG-C9WKB (Windows 8.1 Professional)
GBFNG-2X3TC-8R27F-RMKYB-JK7QT (Windows 8.1 Professional with Media Center)
334NH-RXG76-64THK-C7CKG-D3VPT (Windows 8.1 [Home])
If you can get hold of the installation disk, you can use these keys to install now, and purchase an activation key after 4 months.
The Windows 8 and Windows 8.1 Setup Tools
If you have a valid Windows 8 or 8.1 product key (it used to work for all keys, but now there seem to be some restrictions), you can produce an iso file using the Windows 8 Setup Tool. Download and execute the file Windows8-Setup.exe from Microsoft, enter your product key, and have the tool download the Windows 8 or 8.1 setup files. The tool will then be able to compile an iso file or bootable USB stick from the download. This procedure however has some restrictions, as it will determine the language and bit edition of the download from the system on which it is executed, and doesn't allow to change these parameters.
Windows Free for Students
Those of us who are still at college, and whose institution provides access to Microsoft DreamSpark Premium, are among the especially privileged. If that's the case for you, consider yourself lucky! You'll get Windows 8.1 free!