Update #3: NesterJ v0.71 is now available! Changes include: Some of the buggy mappers were fixed, the speed bugs that varied between ROMs were modified, and an external database reference file has been included in this update.
Update #2: Ruka has now released NesterJ v0.70 which includes a nice speed increase, fixed sound, and also ZIP file support.
Update: NesterJ v0.50 has now been released and includes bug fixes with preliminary sound too- nice work Ruka!
Today Ruka has released a new NES Emulator for the PSP based on the original Nester NES emulator for the PC. Although this initial version does not have sound, the author plans to release the source code for it soon so more people can work on it. Until then, those interested can check out NesterJ v0.01.