Try this great little software – Tangerine! It analyzes the rhythm of your music and generates you a playlist of songs which fit to your training plan. With the right beats per minute (BPM) and beat intensity of your songs you can use faster songs to become faster ;).
It’s all done in your iTunes music library. Right now the software costs around 25$.
System requirements call for Mac OS X v10.4.
Who of you is using it already?