21 Mar 2010
Flex 4 is gold (build 4.0.0.14159)
Hopefully we’ll see an official Flex SDK, Flash Builder & Player 10.1 release this week.
This is the single most exciting month in Flex history 
So many major Adobe products coming out in a single months time.
Flash Builder 4 (incl. SDK)
http://www.adobe.com/devnet/flex/
Standalone SDK:
http://opensource.adobe.com/wiki/display/flexsdk/Download+Flex+4