September 3rd, 2014: For information on what's new in 0.8.9, see the release announcement.
If you are already using 0.8.x, you can install 0.8.9 incrementally by just using "Check for Updates" in your IDE, and applying the update mechanism which will patch your existing install.
From all older versions, you will need to download a full install instead.
To install Android Studio manually:
Windows: https://dl.google.com/dl/android/studio/ide-zips/0.8.9/android-studio-ide-135.1404660-windows.zip (164 MB)
Mac: https://dl.google.com/dl/android/studio/ide-zips/0.8.9/android-studio-ide-135.1404660-mac.zip (164 MB)
NOTE: These .zip files do not contain an embedded SDK install. If you have an existing install of Studio which contains an embedded SDK, if you upgrade by installing one of these zips, make sure you copy over the SDK as well.