If you have a decent mp3 collection , a creative mind and some computer time why not have a play with Mixxx ?
Its a DJing tool for linux , mac and windows which allows you to play 2 mp3's simultaneously and mix them with its built in mixer. You can also apply basic fx and pitchshift up and down to a huge range.
It's very stable and i've got it to work with 2ms latency on my 1.8ghz system which makes it frighteningly responsive yet with enough stability for live performance
Recent enhancements include external midi control , vinyl control , monitoring via a second soundcard and a large collection of skins