html5video.org – Kaltura write, host and run the html5video site. Sort of sums it up doesn’t it. Heaps of information here and this is the first stop you’d probably want to make. Has demos and a blog. Kaltura is open source video service that you can install and run yourself, or pay for them to do it all for you.
Popcorn.js this is a library that provides an event framework for use with HTML5 to provide ways to talk to time based content and webpage elements. Provides the glue for a lot of the better early work being done.
Apple’s “About HTML5 Audio and Video” information from the Safari Developer Library.