After the success of the Free iPod site Gratis Network is starting a new one for the PSP. You only need to complete one offer and get five referrals for this one. Wired has a story on the company if you want some proof that this isn't a pyramid scheme:
http://www.wired.com/news/mac/0,2125,64614,00.html

Here's the link if you're interested:
http://www.freepsps.com