The Wilderness Downtown is a project created by writer/director Chris Milk with the band Arcade Fire and Google. The project was built around the song “We Used to Wait”, giving each user a personalized experience using HTML5 and integrating online tools like Google Maps.
Dev.Opera has a great tutorial on creating a custom HTML5 video player with CSS3 and jQuery that could help you build a very customized player for your web site.
HTML5 Reset is a set of files you can use as a template to start a new project. The HTML file contains a rudimentary HTML5 document structure, with all the every day stuff like title, header, footer, etc. It also uses conditional comments to call about half a dozen IE-specific CSS files, as well as a couple popular IE-correcting javascript files
. You can choose from two versions, the “full version” and one that has just the basic features. Both versions are downloadable here.
Another great example of some of the things that can be done using HTML 5 features: Dale Harvey created a playable HTML5 Pacman.
RGraph is a HTML5 library that uses the canvas element to create a wide variety of graph types: bar charts, line graphs, pie charts, progress bars, and a lot more. You can check some of the examples or read about all its features.