I have also heard of Ring and have heard good things -- Skybell is a competitor. When someone rings the doorbell, you can view a live video feed from your smart phone, and if you choose to, reply (audio only).

I've been playing around with ip cams the past several years and there has been a dramatic improvement in both quality and affordability. In fact, I picked up a few ip cams last week capable of recording at 1080p/30fps for about $62 each. Almost everything I've seen includes integrated IR, which makes night viewing/recording possible (in black and white). Just be sure you don't put this up against a pane of glass, as there will be a reflection. Also... to back up what others have mentioned, POE is really helpful to have (especially if you're going after an outdoor solution), as well as a battery backup.