Qarl and Soulless released a DJ Mixer for the PlayStation Portable.

Features:

MP3 File Browser
Load two simultaneous tracks (one in each plate)
Individual volume control for each track
Crossfader
Control playback for each track individually: Play/Pause and Stop
Visual indicators
Themeable interface
Replaceable sound effects: wav format @ 1411kbs

Thanks to http://www.tehskeen.com/forums/showthread.php?threadid=16876 for the news.

http://psp-ita.com/?module=news&id=34578