I've been looking for a Flash audio player and found a nice one called 1 Pixel Out - Audio Player. The only thing I'm missing is a volume control.
The player is availible as a plugin for Wordspress and it's source code can be downloaded here. It's free to modify due to the GNU-licence status.
If you like to use the player with another platform than Wordpress Mindy McAdams has the instruction.
Here are a few examples. Mixes are borrowed from our friend DJ JayStarSeven.