If you're looking for some sites to play <video> and <audio> using the new elements, I've listed some below. Please add any you know of in the comments:

• A great demo that uses video, filters and CSS Transforms.
• My video test page.
• Opera's video page with demos.
• tinyvid.tv, an experimental Ogg video site.
• Radio New Zealand <audio> support. (You can run the Oggulate script on pages like this one.
• Anne van Kesteren's Fronteers HTML 5 presentation which has <video> embedded in the presentation itself.