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.
Dr. Clue's javascript reference - - a handy repackaging and extension of javascript documentation designed for quick reference as well as detailed study.
ECMA-262: ECMAScript specification - - The official specification for ECMAScript, the vendor-neutral standard for what was originally Netscape's JavaScript.
JavaScript 2.0 at Mozilla.org - - language design page for JavaScript 2.0, which extends JavaScript with classes, packages and types.
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".
JavaScript Object Hierarchy - - A table of the most commonly used JavaScript objects, with all of their properties, methods, and event handlers.