Building a custom HTML5 video player with CSS3 and jQuery
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.
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Audio player with javascript & HTML 5
jPlayer is a great idea that takes advantage of the audio tag in HTML 5 to create an extremely customizable (just HTML and CSS) audio player using jQuery. You can get some ideas by looking at the demos.