编程的一些有用网站

Developer community, answering each other's questions. SUPER valuable resource.
http://stackoverflow.com

Easily share code with others, especially if you want to ask them a question about it. Stackoverflow.com allows integration with this site, which makes it really useful.
http://jsfiddle.net

Community-based code sharing, similar to JsFiddle.net, but with a LOT more features, including a built-in Javascript console.
http://CodePen.io

Creat CSS/HTML tutorial site founded by Chris Coyier.
http://css-tricks.com

Organization producing and managing different web-related standards:
http://www.w3.org

W3C HTML5 Recommendation
http://www.w3.org/TR/html5

Excellent site that keeps track of HTML-related technologies and browser compliance with each feature. Allows you to search for feature, tag, attribute, etc.
http://caniuse.com

Validate your HTML using this W3C.org validator
http://validator.w3.org

Browser usage statistics form w3schools.com. In my opinion, these statistics are very accurate if you want to know which browers are popular with the developer/IT community.
http//www.w3schools.com/browsers/browsers_stats.asp