Node itself : https://nodejs.org/
A great way to get started is with the nodebeginner book.
Felix Geisendörfer has a great site,
Express.js Guide: The Comprehensive Book on Express.js - http://expressjsguide.com
Practical Node.js: Building Real-World Scalable Web Apps- http://practicalnodebook.com
There are some great tutorials out there for Node, I've pulled a few together here.
Part 1 – Introduction to Node.js
Part 2 – Welcome to Express with Node.js and Azure
Part 3 – Building a Backend with Node, Mongo and Socket.IO
Part 4 – Building a Chatroom UI with Bootstrap
Part 5 – Connecting the Chatroom with WebSockets
Part 6 – The Finale and Debugging Remote Node Apps