Reference

Client-Side JavaScript Guide
Books on how to use core and client-side JavaScript.
http://docs.sun.com/source/816-6408-10/

DevGuru JavaScript Quick Reference
List of every command and function with individual page descriptions.
http://www.devguru.com/Technologies/ecmascript/quickref/javascript_index.html

DOM Node and Object Structure Summary
This gives all properties, collections and methods of the W3C DOM that can be reliably used in all major DOM browsers, as well as document.styleSheets, which is very unreliable, but useful if it works.
http://www.howtocreate.co.uk/tutorials/index.php?tut=0&part=28

Dr. Clue's javascript reference
a handy repackaging and extension of javascript documentation designed for quick reference as well as detailed study.
http://www.drclue.net/F1.cgi/JAVASCRIPT/JAVASCRIPT.html

ECMA-262: ECMAScript specification
The official specification for ECMAScript, the vendor-neutral standard for what was originally Netscape's JavaScript.
http://www.ecma-international.org/publications/standards/Ecma-262.htm

JavaScript 2.0 at Mozilla.org
language design page for JavaScript 2.0, which extends JavaScript with classes, packages and types.
http://www.mozilla.org/js/language/js20/index.html

JavaScript and Browser Objects Quick Reference
Free downloadable reference guide to JavaScript objects and properties in PDF format, designed for printing. Covers all versions of JavaScript, and indicates which browsers support each object or language element. From Danny Goodman's book "JavaScript Bible".
http://www.dannyg.com/ref/jsquickref.html

JavaScript Object Hierarchy
A table of the most commonly used JavaScript objects, with all of their properties, methods, and event handlers.
http://archive.devx.com/projectcool/developer/reference/jscript_obj.html

JavaScript R&E Site
reference, syntax, and examples you can use.
http://fluffycat.com/javascript/

Microsoft JScript
Microsoft JScript documentation: JScript User's Guide. Using JScript in Internet Explorer. JScript Language Reference.
http://msdn.microsoft.com/en-us/library/72bd815a(VS.80).aspx

Navioo
Provides a list of all classes of the language's core with navigators compatibility test.
http://www.navioo.com

Woodger's JavaScript Reference
JavaScript Overview as well as coding tips.
http://www.woodger.ca/js_top.htm