This simple Flash-based code from Google embeds the following player controls.
<embed type="application/x-shockwave-flash" width="400" height="27" src="http://www.google.com/reader/ui/3523697345-audio-player.swf" flashvars="audioUrl=http://yourdomain.com/audio_files/song.mp3" quality="best"></embed>
Features: Flash-based. Plays single track/file.
Positive: Great for the occasional sound clip & large files. Easy to swap in your own MP3 file paths.
Negative: Cannot modify colors/dimensions. Sticks out like a sore thumb.
Source: Google Reader Player