You probably know that one of the best Android internet browsers, Chrome, was actually developed by Google. There is probably no need to mention the search engine, YouTube, which is also owned by Google, is also widely known. I will take a wild guess and expect you to know about Google Earth, the image cartography of the whole Earth, partly even in 3D imagery. Additionally, I would expect you to know about the Google mail service and the Google Drive, their cloud service. The Google Calendar is mostly pre-installed in every Android device. You may have already used the only viable map app, Google Maps, there is nothing like it, with the add-on Google Street View.
But there are also other Google Apps that are not so popular, or rather, people for some reason do not use them. Nevertheless, these apps are excellent and do warrant a closer inspection. Did you ever hear about Google Currents, an application that is pretty similar to the Flipbook, but perhaps even better? (https://play.google.com/store/apps/details?id=com.google.android.apps.currents) In the glossy magazine-like interface you can read and review all your favourite magazines and newsfeeds in high quality.
Another one of such hidden Google gems is Google Goggles. (https://play.google.com/store/apps/details?id=com.google.android.apps.unveil) Originally developed as a QR code scanner, this app has become more than a simple sideliner. With it you can scan barcodes and get product info. You can point them towards famous landmarks and receive info about that particular place. You can instantly translate a foreign language text, such as a menu in a French restaurant, and have translated text right there. It can even OCR texts for you, recognize famous paintings, CDs, DVDs, books, even advise on similar products. This is definitely an applications worth having, if you do not have it already.
Just like the already mentioned Polaris Office, Google QuickOffice allow you to edit and view MS Office documents and PDF files. (https://play.google.com/store/apps/details?id=com.quickoffice.android) The big plus is that you can load them up on Google Drive and edit them there, from where you can also easily email it per Gmail. While it is not as extensive as Polaris Office the integration with other Google services makes it worth your while.