I believe that the <canvas>, <audio>and <video> tags will make the web a pretty exciting place. A lot of Flash components will be rewritten or converted into Javascript+HTML5 Object components making available more reusable elements for a graphical and interactive web, all being open sourced (javascript) and with no extra plugins needed.
Some places where we can already see (or will) the use of HTML 5 tags and javascript on those elements are:
- GMail Mobile for iPhone and Android
- Yahoo! Pipes
- Bespin, a code editor created by Mozilla lab, they basically rewrote the text editing component using the canvas tag so that its a high performance text editing component, with a nice look, selection highlighting, new scrollbars, command support, it can be extended with your own commands (reminds me of emacs)
- Google Waves
- Some blogs that are already using the <article>, <nav>, <footer> and other new HTML 5 tags
- YouTube is getting ready for the video tag