Here are some useful resources for who is trying to learn or improve your HTML, CSS and JavaScript skills:
Dive Into HTML5
An amazing book about HTML5 for free, can you believe it? Go right now to diveintohtml5.org to learn about the HTML history, new HTML5 tags and much more.
WHATWG Community
The WHATWG group is the one who is creating the HTML5 specs. There’s a lot of useful information about HTML5 specs, a blog that you definitely should read, demos, etc.
MDN – Mozilla Developer Network
A lot of contents and reference documents about HTML, CSS and JavaScript. You really need to bookmark it.
HTML5 Glossary – HTML5 Doctor
A great list of HTML5 tags, with code snippets and examples. Really useful when you need to check what tag fit your needs.
HTML5 Outliner
An HTML5 outliner that shows if your HTML5 document headings structure are correct.
HTML5 Boilerplate and HTML5 Reset
Tired of creating always the same HTML base structure? HTML5 Boilerplate and HTML5 Reset are both an HTML base templates, so you can start your project with a good set of HTML, CSS and JS files. Also, is a good resource to study the HTML5 and CSS3. Go take a look on it now!
Modernizr
Modernizr is a JavaScript library that allows you to check if the client browser has support to some features of HTML5 and CSS3, so you can decide what to do if the client doesn’t support a specific feature that your website uses/needs.
CSS3 Pie
This guy makes IE6-8 to render some of the new CSS3 properties. You really need that to make your life easier when trying to make your site to work on IE browsers.
CSS3 Please
Some awesome CSS3 cross-browser code snippets like round, shadow, gradient, transitions, etc.
More
You should take a look on this guys too:
That’s it. Now, go on and make a lot of stuff using all the power of HTML5, CSS3 and JS!