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.
A DHTML shell that allows you to query the current browser window. Includes command line JavaScript execution, mouseover DOM query, CSS input, tab completion, profiler and object inspection. Can be configured to run off a bookmarklet, and works in IE, Firefox, Safari and Opera