DJMAX is a Rhythmic game developed by Pentavision. It's platform is available for PSP, Computer, Mobile Phones and Arcade.
Their latest release for PSP is DJMAX Portable 3 which was released last October 14, 2010.
Here's a bit of a trailer for DMP 3.
And a bit of a gameplay:
Oh, and if you're a bit confused with the remix system, look at this one:
Hope you enjoy being a DJ with this game!