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.
April 16, 2014: Android Studio 0.5.5 Released. See the Canary channel for more.
March 25, 2013 - Eclipse ADT 22.6.2 Released
For more information, see the release notes.
March 4, 2014: Android SDK Tools 26.1 Released. See http://developer.android.com/tools/sdk/tools-notes.html for more.
For more information on the status of each of our branches, see the Release Status page.