There are five PSP emulators in the work at the moment, and they are :

• JPCSP is a Java PSP emulator that available for Windows and Linux. Obviously it needs Java JRE installed. Here's the latest version :
  - jpcsp v0.1 revision 812 for Windows
  - jpcsp v0.1 revision 812 for Linux64
  
  
  
• PCSP, authored by same JPCSP authors, this version is not written in Java. Quoting the author PCSP is "way less advance than jpcsp" but  "kinda faster". Here's the latest version :
  - pcsp rev201
  
  
• emu-sam is developed by Actarus, although still actively developed currently there's no download to try, only some progress report. There's version 1.0.0.1 which can be download from Ngemu here, I've seen 1.0.0.2 but can not find download link.
  
  
• pspplayer, 
  
  
• mfzpsp is project with a goal to emulate the Playstation Protable Architecture on a
  Low Level Basis. Believe me I don't know what that means. The author is currently busy with his school schedule so this project is on halt but not freezed.
  

I suggest you start with JPCSP, it's the most actively developed with new version released frequently (compared to the others).


keyword: free, psp emulator, info, download link