The iDoorCam ($130) is an easy-to-install device that connects to your existing doorbell wiring using only a screwdriver in just a couple of minutes.
It’s WiFi-enabled, and contains a button, day- and night-vision camera, microphone, speaker, and motion sensor, letting you see and communicate with whoever rings your door.
It pairs with an included iOS app, letting you monitor your door from inside your home, at the office, or away on vacation.
Only problem is mounting. I think most people are like me where the current doorbell is too close to the door frame to put this up.