Just after initially unveiling Google Play Services, Google has made the APK installable directly from the Play Store.
For those who missed the announcement, Google Play Services is an APK rolling out automatically to devices running Android 2.2+ that will allow Android apps to easily integrate with Google services like Google+. At present, the app (which is in version 1.0 "Asiago") includes components and relevant client APIs for OAuth 2.0 authentication, Google+ sign-in, and Google+ +1 buttons. Google assures users that "we anticipate more Google services to be continuously added, so be on the lookout for these updates."
The Google Play Services app began rolling out through the Play Store automatically, primarily in order to keep updates to the service independent of carrier or OEM updates. It can now be downloaded directly from the Play Store, however, and apps reliant on Google Play Services can automatically take users to the download page using an unsearchable "deep link" in the Play Store when needed.
The app's rollout is expected to complete within a week, but if you're for whatever reason itching to get the Google Play Services app on your device right away, or ever need to download/update it manually in the future, hit the widget below.