The August DirectX SDK was released today (shh, don't tell them it's September). This brings with it the first official release of DirectX 11!
You can download it in all of it's glory here:
August DirectX SDK
Note: In order to run the DX11 samples on Vista, you need a patch. Unfortunately, that patch is not yet available, but when it is it should be available here.
In very related news, it looks like the first DirectX 11 GPUs will be available this month. The Radeon HD 5850 will be $300, the Radeon HD 5870 will be $400, and the Radeon HD 5870x2 will be $600.
Read more here