What are some of the best reference sites for HTML and JavaScript programming

I find the Mozilla Developer Network very helpful.

Steve

MSDN has a lot of reference materials for web development. It contains only IE-specific information which can be either an advantage or a disadvantage depending on what you are looking for. Here are direct links to the HTML/CSS (includes DOM), JScript (Microsoft flavor of ECMAScript aka JavaScript) and VBScript. The documentation is very well written, and is a great source for answers to DOM/JavaScript questions, since they tend to be mostly the same across browsers.

Also, as references go, let's not forget the official specifications for HTML, CSS, and the myriad of other standards specified by W3C.

Dev Opera is a great resource, especially the Web Standards Curriculum. Another one is HTML dog.

I always check www.zvon.org, especially the references section.

HTML Code Tutorial is a decent site, and its Quick List page helps me sometimes.

A really helpfull tool for Firefox (with Firebug installed) http://tools.sitepoint.com/codeburner/

For rapidly find documentation on sitepoint reference.

Best resources to learn JavaScript

I have been catching up on modern Javascript techniques, and learning some handy tricks, by running, reading and editing GreaseMonkey scripts from userscripts.org.