Jpcsp is a PlayStation Portable emulator for PC, started by shadow (the same great person that made PCSX & PCSX2) and joined by a great team.
Jpcsp is the first psp emulator written in java, allowing to play your psp games on a PC.

The project is still a beta release, but currently more than 50 games are already playable. See the list here.

Latest official version: 0.4
Based on r1287 December 23 2009

Unofficial recent SVN builds can be found at http://jpcsp.org/forum/viewforum.php?f=21

Other PSP emulators:
http://code.google.com/p/emu-sam/
http://code.google.com/p/pcsp/
http://code.google.com/p/pspplayer/
http://code.google.com/p/mfzpsp/