You can find a complete list of working/not working homebrew [here].  But just to get you started, here are a few popular homebrew programs that are known to work so you can get started experiencing the full potential of PSP homebrew:

Super Nintendo Emulator
Sega Genesis Emulator
Atari Lynx Emulator
Vortex
Throttle-X
Squarez
Spider Solitaire
PSPRhythm
FileAssistant

And for all of the PSP enthusiasts reading this, here is a special message from Fanjita himself:

I just want to say thank you to all of the PSP lovers out there for supporting us. Keep checking back here at PSPUpdates — our goal is to continue to give all PSP owners with all firmware versions the ability to play homebrew.

Download: [eLoader for 2.01 / 2.50 / 2.60 Firmware]