Mixpanel, Userfox, Customer.io, Intercom.io, Help Scout, Desk.com, Olark, and UserVoice are all tools that come to mind. It comes down to preference a bit. The engagement features in Mixpanel are probably my favorite for setting up drip email campaigns and it's a really great analytics tool to start with. I'm of the opinion that great customer service begins with understanding the customer and how they're using your product.

For books, I've heard really good things about "Delivering Happiness." I'm a fan of Seth Godin as well, but he writes more about marketing. I think the ideas translate fairly well though.