Siri will have a couple great new features in iOS 8. One is hands-free operation, such that you can simply say "Hey Siri" and Siri will respond. This, of course, will be especially useful if you're in your car.
Another feature is integration with Shazam, the music recognition service. When some music is playing, you can simply say, "Hey Siri," and then ask what's playing, and Siri will tell you.