Mozilla Developer Network Really nice resource for HTML, including tutorials, element reference, forms guide, CSS and examples. Written by an organization that cares about HTML and standards.
Get Bootstrap The official source for the Twitter developed front-end HTML, CSS and typography libraries. It's automatically installed and enabled in ASP.NET MVC 5
Using Browser Tools A quick summary of how to view HTTP headers and info using your browser.
Postman A fantastic tool for testing your REST interface, web service or AJAX calls.
PUT or POST A short summary on faulty assumptions in many RESTful articles.
Let's Build a Web Server If trying to understand what ASP.NET MVC 5 is doing for you, take a look at this clear example written in Python. Diagrams are almost as good as in Learn You a Haskell for Great Good!