[disclaimer: I work at Google]

https://cloud.google.com/customers/

Spotify, SnapChat, eBay are the examples I usually give when asked that question.

I'm not sure what numbers I am allowed to provide for any of them, but there's some public information available that gives you a sense of the scale involved:

https://labs.spotify.com/2016/03/03/spotifys-event-delivery-...

https://www.itnews.com.au/news/do-not-fear-the-cloud-ebay-mi...