JavaScript

Preloading images. This example shows how to wait for all images to be loaded.
Hiding a column in a table
Search and replace
Checking if JavaScript is enabled
Dynamically creating style sheets
A javascript menu for Internet Explorer (that is: not cross browser)

Variables

Events

Elements (Accessing and Manipulating Elements (nodes) in the DOM)

Form related stuff

The date object

Requesting XML (or text) from a server with JavaScript

Finding Text with JavaScript

Launching MS Word with JavaScript

Setting and reading cookies

Microsoft's JScript Reference

Pseudo Classes Fix for Internet Explorer': Simulating :hover and :active with behaviours.

Claus Madsen(?) has a page with right mouse click handler that opens an "own" window.

Using the XML HTTP Request object: Internet Explorer on Windows and Mozilla provide a method for client side javascript to make HTTP requests. This allows you to make HEAD requests to see when a resource was last modified, or to see if it even exists. It makes your scripting options more flexible allowing for POST requests without having the page change, and opens up the possibility of using PUT, DELETE etc.

Dynamically updating SVG based on serverside information

Formatting numbers.

Closures.

(Re)-introduction to JavaScript by Simon Willison.