On Monday of this week, Microsoft officially announced the editions of Windows 8 that will be available. [They also confirmed that it would be called Windows 8. The release of the logo two months ago was a pretty good indication but it's for sure now.]
They are: Windows 8 and Windows 8 Pro. Each will be available in 32-bit and 64-bit versions.
Very simply, Windows 8 Pro is for techies and businesses. Windows 8 is for everyone else.
I'll save you the rehash and just send you to Microsoft's post:
Announcing the Windows 8 Editions [Microsoft: The Windows Blog]
Check out the excellent table mid-way down the page that compares the availability of major features between the Windows 8 editions.
I like the simplified options, at least compared to previous versions of Windows. What do you think?
ETA: There will also be a Windows 8 RT (aka Windows on ARM or WOA) that will only be available pre-installed on computers (primarily tablet computers) powered by ARM processors. There will also be an enterprise edition called Windows 8 Enterprise. The server version of Windows 8 will be called Windows Server 2012.