Paul Irish
Some exciting libraries have cropped up lately:
Paper.js - a vector graphics scripting framework that runs on top of <canvas>. It is based on and largely compatible with Scriptographer, a scripting environment for Adobe Illustrator. If you've ever wanted an object model to sit above canvas, take a peek.
RPG JS- a role playing game framework for 2D games that leverages EaselJS for its scene graph. Can use many RPG Maker XP assets to get a quick head start.
Chop Slider - making heavy use of CSS transitions and effects to get impressive transitions between states.