There is a massive thread on PSPISO with links to every known PSP Title that can be downloaded from the Playstation Network. The downloads are open for everyone to download, but they are encrypted so that (supposedly) users who did not buy it cannot run it on their PSPs.

With the discovery of the PSP signing keys, this encryption system has become all but worthless, and there is no longer any need to torrent anymore; simply download the game directly from Sony, decrypt it, and play it for free. (At least that's what we think happens.)

• PSPISO - Community PSN Share Thread