I'm looking for good documentation about HTML5 does anyone know where I can find this ?
Other than w3c, Wikipedia tends to be pretty good at having an overview for technical standards: http://en.wikipedia.org/wiki/Html5
It's true the the HTML5 spec can be a bit heavy for web developers, given that it is more geared towards browser vendors
At the risk of being told off for self-promotion, though the site is very relevant, I run a site with a few clever guys called HTML5Doctor where we take elements and explain them, with examples, so you can understand HTML5. We also have a glossary and decent size archive of articles all to do with HTML5.
You may also be interested in "When can I use...", a page that details what elements, CSS properties and APIs can be used in which browsers. Very handy for working out if you can afford to implement these new HTML5 features on your site.
Dive Into HTML 5 is a good introduction to some features, written in a more conversational tone. Much less dry than the actual spec.
It's a work in progress though, so only some features are covered.
There is an official developers version of the spec at http://dev.w3.org/html5/html-author/
I wrote article about this on my blog, check it out: http://deanhume.com/Home/BlogPost/html5-input-types/25
Also, there is the Html 5 slide deck on html5rocks.com Check it out: http://slides.html5rocks.com/#slide21