Ivo Wetzel covers some of the quirks of the JavaScript language. Some of these cause subtle bugs, some overturn conventional wisdom. It covers toString on numbers. Covers the advanced JavaScript features such as prototypal inheritance, this, closures, anonymous wrappers, type-casting, automatic semicolon insertion and hoisting of function and variable declarations.
Matt Kruse's JavaScript Toolbox presents a number of excellent best practice ideas including: using var, feature detection, when to use square bracket notation, avoiding eval, referencing forms and form elements, avoiding the with keyword, using onclick instead of JavaScript pseudo-protocol, using unary + to type convert to numbers, avoiding document.all, not using HTML comments in script blocks, avoid cluttering the global namespace, avoiding prototype.js, avoiding synch Ajax calls, using JSON and the correct way to use script tags