html

Layout Gala: a collection of 40 CSS layouts based on the same markup and ready for download!

This is awesome! Like CSSZenGarden for generic layouts. I’ll definitely be using this. They all validate and use good code.
&what; — Discover Your Character
HTML5 Cross Browser Polyfills · Modernizr/Modernizr Wiki
Recipe – schema.org
Simply Testable professional automated front-end web testing
Modernizr

This is awesome.
Word 2007 HTML and CSS Rendering Capabilities in Outlook 2007 (Part 1 of 2)

Marginally helpful reference for evil Outlook 2007.
HTML-Ipsum

Handy! This site has dummy text formatted with various HTML codes.
persistent checkbox code

I’m using this for a Church Office feature I’m working on.