There's a whole universe of tools out there for helping people make mp3s play in web pages. I conducted a quick survey to collect the following samples. Feel free to add more entries as well as usage tips and warnings for the existing ones. -- Greg
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Yahoo Media Player?

http://developer.yahoo.com/mediaplayer/?

Pretty much the state of the art in this space. Reads a ton of different playlist formats. Detects in-page links to XSPF and chunks of inlined hAudio.?

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del.icio.us playtagger
http://del.icio.us/help/playtagger

Yahoo easylistener
http://next.yahoo.net/archives/32/easylistener

http://www.myflashfetish.com/
site to pick a design, customize, and setup a playlist for flash embed player

Flash MP3 Player for MySpace?

http://www.myspace-gen.com/flashmp3player
with customization and playlist construction

FLAM Player

http://www.flamplayer.com/
"This is an mp3 player built in Flash, and so, it can be embedded in an Html page. It works using PHP and MySQL. The database stores the authors and tracks characteristics, the PHP scripts manage the communication between the Flash player and the MySQL database.

?includes a back-end allowing the fast addition of tracks, the edition of authors or tracks characteristics, the creation of playlists and the simple integration of the player in a page."
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JW MP3 Player
http://www.jeroenwijering.com/item=jw_mp3_player
"The JW MP3 Player (built with Adobe's Flash) is the easiest way to add live music or podcasts to your website. It supports playback of a single MP3 file or an RSS, XSPF or ASX playlist, a wide range of flashvars (settings) for tweaking both behavior and appearance and an extensive, documented javascript/actionscript API." - used on hype machine

Playa?

http://candyscript.com/projects/playa/
-discontinued for being too similar to soundmanager2

http://www.1pixelout.net/code/audio-player-wordpress-plugin/
-uses the standard rounded-corners expanding player
-use outside of wordpress: http://www.macloo.com/examples/audio_player/

Zuardi XSPF player?

http://musicplayer.sourceforge.net/

SoundManager 2?

http://www.schillmania.com/projects/soundmanager2/
"SoundManager 2 is a Javascript Sound API which talks to Flash, effectively mapping most of Flash 8's native sound capabilities to Javascript. It enables web developers and front-end engineers to programmatically control sound in a cross-browser/platform way, using a language they already know.
In short, "It's Javascript Sound for the Web."

PodBean
http://www.podbean.com/podcast-blog-embeddable-mp3-flash-player
single or playlist versions

PoqBum
http://player.poqbum.com/player/player_type.php

Wimpy
http://www.wimpyplayer.com/
Streaming players

Hoover Web Design
http://www.hooverwebdesign.com/mp3-players.html
buncha goofy myspace-intended ones

mirPod
single: http://www.mirpod.com/blog.phpid_blog0751&id_article075336&lang=en
XSPF: http://www.mirpod.com/article.phpid_article075198&lang=en

Talkr Radio
"Talkr Radio accepts an RSS feed as input, places its posts? titles in the Flash player?s playlist and converts and plays those text-only posts as audio."
setup wizard: http://admin.talkr.com/wizard/

Ephonic
http://www.e-phonic.com/mp3player/documentation/
good docs

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Mashable Flash MP3 Player
http://codes.mashable.com/flashmp3player
looks familiar

Simple
http://www.ericzhang.com/mp3.php

Google Mail
http://labnol.blogspot.com/2006/08/google-mp3-player-found-in-gmail.html
Apparently this used to work outside of gmail