DIVE INTO HTML 5
http://diveintohtml5.org/

html5.org
http://html5.org/

[W3C]HTML5
http://www.w3.org/TR/html5/

[W3C]HTML5 differences from HTML4
http://dev.w3.org/html5/html4-differences/

HTML5中国
http://html5cn.net/

W3school HTML 5教程
http://www.w3school.com.cn/html5/

<html>5doctor
http://html5doctor.com/

HTML5 (including next generation additions still in development)
http://www.whatwg.org/specs/web-apps/current-work/multipage/

Google HTML5 ROCKS
http://who.is/whois/html5rocks.com/