Dan Frakes compiled a list of his favorite new features in iOS 8. You may already know most of these, but having them all together in one place is very helpful, and some features may have slipped your notice.
I completely agree with Dan about the usefulness of the new “Hey, Siri” feature. I wasn’t expecting much from it, but I use it in my car all the time — it’s turned my car into a voice-activated command center.
Dan’s article is available on his website.