The purpose of this list is to provide dates for releases, so those looking for drivers that are compatible with a release have a date to go by.  The list is by no means complete, suggestions for inclusions are welcome.

FOUND THIS LIST that's much better than mine:  http://blogs.technet.com/mrsnrub/archive/2009/08/04/windows-nt-history.aspx

NOTE:  SP0 is the initial release of the OS.  Most information came from Wikipedia.

Windows 7 (Windows NT 6.1)

SP1
- Final - TBD (1st ½ of 2011)
- RC - October 2010
- Beta ~ early July 2010

SP0
- Final (GA) - 22 October 2009
- RTM - Late July 2009

- RC - Public - 5 May 2009
- RC - Connect/MSDN/TechNet - 30 Apri 2009
- Beta - 9 January 2009

Windows Server 2008 R2 (Windows NT 6.1)

SP1
- Final - TBD (1st ½ of 2011)
- RC - October 2010
- Beta ~ early July 2010

SP0
- Final (GA) - Around the time of Windows 7 GA

- RTM - Late July 2009

- Beta - 7 January 2009

Windows Server 2008 (Windows NT 6.0)
SP0
- Final - 27 February 2008

Windows Vista (Windows NT 6.0)
SP2
- Final - May 2009

- RTM ~ 30 April, 2009
- RC ~ March, 2009
- Beta - 29 October 2008
SP1
- Final - 4 February 2008
- RC - 10 December 2007
- Beta ~ 4 November 2007
SP0
- Final - 30 January 2007
- RTM - 30 November 2006
- RC - September 2006
- Beta - July 2005

Windows Home Server (Windows NT 5.2) - 7 January 2007

Windows Server 2003 R2 - December 2005
Windows Server 2003 (Windows NT 5.2) - 24 April 2003

Windows XP (aka Windows NT 5.1)
SP3
- Final - 6 May 2008
- RTM - 21 April 2008
SP2 - 6 August 2004
SP1a - 3 February 2003
SP1 - 9 September 2002
SP0 - 25 October 2001

Windows ME - September 2000

Windows 2000 (aka Windows NT 5.0)
Update RollUp 1 - 13 September 2005
SP4 - 26 June 2003
SP3 - 29 August 2002
SP2 - 16 May 2001
SP1 - 15 August, 2000
SP0 - 17 February 2000
- RTM - 12 December 1999
- RC - July 1999
- Beta - September 1997

Windows 98 SE (Second Edition) released in 1999

Windows 98 released on 25 June 1998

Windows NT 4.0 released to manufacturing on 29 July 1996 (public release on 24 Aug 1996)

Windows 95 released on 24 August 1995

Windows for Workgroups 3.11 was released on 11 August 1993
Windows NT 3.1 arrived in Beta form to developers at the July 1992
Windows 3.0, released in 1990
Windows version 2 came out on 9 December 1987
Windows version 1.0, released on 20 November 1985