The new and much improve download page for the Windows Azure SDK (http://www.microsoft.com/windowsazure/sdk/) has links and a history of all the older releases. It's missing the CTP releases since they are no longer supported in our production environment. I thought I'd put together a complete list of SDKs including CTPs since the first CTP way back in October 2008 (hotfixes not included)

Date Version Notes
September 2011 1.5 overhaul of the compute emulator internals
August 2011 1.4.1 refresh Tools only refresh
April 2011 1.4.1 WebDeploy Plugin (CTP)
March 2011 1.4 Mostly Bug fixes
November 2010 1.3

Admin access, Full IIS, Remote Desktop, VM Role CTP, improved Diagnostics, Windows Azure Connect CTP
June 2010 1.2 .NET 4.0 Support, Fixed Ports, Intellitrace
February 2010 1.1 Mostly bug fixes
November 2009 1.0

First Official Production SDK,Win 7 Support, Introduction of Windows Azure Diagnostics, Inter-role communication
May 2009 CTP 4

VS2010 Beta Support improvements to devfabric/devstore

Internal endpoints
March 2009 CTP 3 Support for native code and Fast-CGI announced at MIX 2009
January 2009 CTP 2 Mostly bug fixes
October 2008 CTP 1

The first SDK release at PDC 2008

What you can see is that we've been pushing out roughly 3-4 SDKs a year. I've had the luck to be on the team since the first SDK release in 2008. In the process, I've learned  many things around versioning/compatibility, servicing, live site support, test prioritization and a few things about cloud computing as well. 

I'll try to share some of what I've learned in those areas over the next few posts. Please, stay tuned.