Don't know if discussion about hacked PSP's is really allowed on here, but if you do have a hacked PSP, or plan to hack it...
Psp Rhythm is pretty much the best PSP app ever created. Its a 16 channel step sequencer that uses samples to make music. While it does have a few limitations, its overall extremely versatile and ingenius. The ability to write down ideas and start songs wherever you bring your PSP is invaluable, and its a hell of alot of fun being able to just start jamming stuff out wherever you are.
http://www.psprhythm.com/
The screenshot doesn't show it, but it has a sort of pseudo-piano-roll step sequencer that lets you pitch notes, as well as some rudimentary sample-looping and enveloping possibilites.
Anyways, if you do have a hacked PSP, its essential. If you don't have one, it makes getting one awfully tempting.
