I wanted an HTML5 audio player on my new site, since a lot of mobile devices can't handle Flash players. This is the best and most attractive I've found. The latest version of this plug-in seems to have resolved some Jquery Library bugs that rendered an earlier version unusable.
I like the versatility of having four different types of players available: widget, playlist, single-song and pop-out. The latest version also offers nice options for customizing the color scheme.
Two additions would make it even niftier: the option to add a border around the player (which can only be done right now by modifying the css stylesheet) and more options to position a player in a page layout. I'd love to see those in the next version.
It would also be nice to have an option to play Ogg Vorbis files as well as MP3s, so the player would work in Firefox. The good news is that it seems to work on every other kind of browser.