March 19th, 2015: For information on what's new in 1.2 preview 3, see the release announcement. For additional information about Android Studio, see the main developer site.
The release is available in both the canary channel and the dev channel, so you can check for updates via Help > Check for Update... (on OSX, look in the Android Studio menu). This will download and install a patch rather than download a full IDE image. For all older other versions you will need to install it from scratch by installing one of the below .zip files.
Windows: http://dl.google.com/dl/android/studio/ide-zips/18.104.22.168/android-studio-ide-141.1793788-windows.zip (252 MB)
Mac: http://dl.google.com/dl/android/studio/ide-zips/22.214.171.124/android-studio-ide-141.1793788-mac.zip (250 MB)
Linux: http://dl.google.com/dl/android/studio/ide-zips/126.96.36.199/android-studio-ide-141.1793788-linux.zip (249 MB)