The current stable release is version "r20" of the SDK Tools and ADT 20.0.3. You can download the official bits from http://developer.android.com/sdk/index.html.
We are currently developing r21 and ADT 21 in the AOSP git trunk.
If you want to build it yourself, follow the instructions in the Build Overview document. Recent user-visible changes to the trunk are listed in the Recent Changes document.
For Studio preview channels, see the Android Studio Downloads page.
For more information on the status of each of our branches, see the Release Status page.