Google Now can do some pretty fancy stuff, but one thing it sucks at is actually listing its own capabilities. Just like keyboard shortcuts, if you don’t know they exist, you can’t try and show them off to your friends.
Ok-google.io is a new site that keeps a complete, always-up-to-date list of Google voice commands. There’s 150 different commands, with over a thousand examples given. I had no idea even a tenth of these existed.