AudioCodex is an audio player for OS X that lets you manipulate the sound in terms of effects in real time and has added visualization facilities. Its a very powerful piece of software and has a suitable price point. There is a free 30 day trial so you can check it out.

Beatport and Native Instruments have released a free audio player with DJ functionality. Based on Native Instruments Traktor and available on both Windows and OS X the software allows you to play, manage and mix your audio collection.