Dive into HTML5
Free web book with a great overview of all HTML5 features.
Appe HTML5 Showcase
Great showcase of HTML capabilities from apple. Source code is a bit proprietary and hard to understand.
De-facto resource for all things web, their documentation of HTML5 standards. Usually useful although sometimes incorrect.
The blog for the Webkit project (HTML5 backend of regular and mobile versions of Chrome, Safari, etc.) Great examples of CSS3 features.
HTML5 expert Thomas Fuchs’s blog. Amazing amount of info. Updated frequently, and offers a number of HTML5 classes.
Font Squirrel @font-face Generator
Awesome @font-face generator that gives you the font files, CSS and examples for (almost) any font you throw at it.
Making an iPad HTML App Really Fast
Post on Mir.aculo.us that walks through the basics of creating an HTML5 iPad app and optimizing it. Great overview.
Touching and Gesturing on the iPhone
Great overview of touch events.
Overview of creating offline apps, which is the basis for HTML5 web apps that work without internet connection.
Creating an HTML5 Web App
Shows how to create a web-app and a lot of grew things to consider. Aimed at iPhone but translates pretty much exactly to iPad.
Article I wrote as an overview of how memory management works on the iPad and how to deal with it.
Framework for dealing with SVG based graphics.
HTML5 Canvas based port of the extremely popular Processing language. Great for creating interactive canvas based applications.
JQuery-based mobile framework, great for create simple UI based apps, still a bit under development. Not so great for custom apps
Probably the best all-inclusive solution for creating cross-platform mobile apps. Based on the Ext.js framework, Sencha uses an extremely different system for creating apps. Similar to jQtouch (although more complete/powerful) in that it is easy to make simple UI based applications, but not great for custom apps.
MooTools (My Object Oriented Tools)
My favorite (and in my opinion the best) general framework for creating custom HTML5 apps. Supports full object-oriented programming (classes, constructors, extending and implementing classes, etc). Not as large of a user base as jQuery, but a lot more serious/experienced users. Great comparison between MooTools and jQuery (by the creatore of MooTools) at http://jqueryvsmootools.com/