Web Share API
This specification defines an API for sharing text, links and other content to an arbitrary destination of the user's choice
Animate.css
Fluidity
Modern Web Development
HTML5 Custom Data Attributes (data-*) | HTML5 Doctor
Custom data attributes are intended to store custom data private to the page or application, for which there are no more appropriate attributes or elements.
Ultimate List of HTML5 and CSS3 Tools | Admix Web
great tools that can help you to master these new features of both HTML5 and CSS3
ProtoFluid - HTML5 and CSS3 Web App Prototyping
Test your @media queries and web app on various screen sizes
Safari Reference Library
The Safari Reference Library provides detailed information for web developers on iPhone, iPod touch, Mac, and PC. These resources include guides and articles, API reference documents, sample code, release notes, and technical notes. Use these resources to learn about Safari's developer tools, visual effects, HTML and CSS support, JavaScript and DOM support, and other features and technologies. The library is organized by Topics and Resource Types
Let’s Take This Offline - Dive Into HTML 5
In depth HTML5 storage - excellent as usual
HTML5Rocks - Best Practices for a Faster Web App with HTML5
Google's tips and playground
Announcing an HTML5 mobile app framework for touch devices
check this out