James Shore's fantastic (and well-recommended) Let’s Code: Test-Driven JavaScript is a screencast series designed to imbue JavaScript developers with test-driven practices. He's now released Object Playground, "a free video and visualizer for understanding object-oriented programming".

The visualizer is very cool: it runs actual JavaScript code and graphs the object relationships created by that code. There are several preset examples and you can also type in arbitrary code of your own.

Object Playground

It contains demonstrations of a basic class, classical inheritance, Resig inheritance and a deeply intertwined Inception class! Make sure you zoom out or use a widescreen monitor for full effect.