Jon Raasch's notes on Nicholas Zakas's Google Tech Talk "Speed Up Your JavaScript" in which he covers basic performance improvements like local variables for more expensive lookups, avoiding for in loops, casting DOM array-like objects into proper arrays, avoid touching the DOM, use classes to change CSS instead of inline styles.
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.
Erik Arvidsson warns against extending the JavaScript Object with Object.prototype, as it can lead to breakages in third party code when they use the for(key in obj) method of iterating through any class (since they all are subclasses of Object). Instead Erik recommends extending the classes that directly benefit from the extending functions, and treat Object as a final constant. Erik also suggests that hashes and associative arrays should be done in JavaScript using Object, not Arrays.